shall i tell you where the dead are?

Shall I tell you where the dead are?

Shall I tell you where the dead are?
You won't find them in the sky
Their faces don't grace clouds,
or rest in a person's eye

Shall I tell you where the dead are?
You won't find them on the street
If you missed them the first time,
then there's no chance they'll repeat

Shall I tell you where the dead are?
You won't find them on a wall
A picture is but a picture,
and that just won't do at all

Shall I tell you where the dead are?
You won't find them in a book
Better catch them while they're living
Better have yourself a look

Shall I tell you where the dead are?
You won't find them in a voice
They've moved on to different pastures,
but not one is there by choice

Shall I tell you where the dead are?
Very well, you'll get your way
The dead rest in the ground,
and it's there they'll always stay

nano mean

Nanotechnology

(sometimes shortened to "nanotech") is the study of manipulating matter on an atomic and molecular scale. Generally, nanotechnology deals with structures sized between 1 to 100 nanometre in at least one dimension, and involves developing materials or devices possessing at least one dimension within that size. Quantum mechanical effects are very important at this scale, which is in the quantum realm.

Nanotechnology is very diverse, ranging from extensions of conventional device physics to completely new approaches based upon molecular self-assembly, from developing new materials with dimensions on the nanoscale to investigating whether we can directly control matter on the atomic scale.

There is much debate on the future implications of nanotechnology. Nanotechnology may be able to create many new materials and devices with a vast range of applications, such as in medicine, electronics, biomaterials and energy production. On the other hand, nanotechnology raises many of the same issues as any new technology, including concerns about the toxicity and environmental impact of nanomaterials,[1] and their potential effects on global economics, as well as speculation about various doomsday scenarios. These concerns have led to a debate among advocacy groups and governments on whether special regulation of nanotechnology is warranted.

President opening lines repeat of 2010: Yechury

NEW DELHI: Does the government know when the new decade actually began? No, said CPM's Sitaram Yechury, pointing out that the opening lines of President Pratibha Patil's address to Parliament this year were the same as in 2010.

Taking several digs at the Union cabinet, which approves the presidential address, Yechury said on Wednesday that the first sentence of the President's speech on February 22, 2010 read: "My greetings to you as you assemble here today for the first session of both houses of Parliament in the new decade.'' And this year, she said, "I welcome you to the first session of the new decade.''

"This government is in a sense of stupor...it's unable to make up its mind when the decade begins! It's an amazing thing. The President's speech actually reflects a directionless drift that this government has been gripped in,'' Yechury said in the Rajya Sabha while speaking on the motion of thanks to the President.

With this, the CPM leader mounted a blistering attack on government for creating avenues for corruption and promoting crony capitalism, demanding that concessions worth several lakhs of rupees being given to corporates and high-end taxpayers should instead be used to narrow the rich-poor gap.

BJP's Ram Jethmalani too launched a scathing attack against the government over the issue of black money saying that the government was not interested in getting back over $1,500 billion dollars.

However, in Lok Sabha, Jagdambika Pal (Congress) praised government's vision to alleviate the misery of the common man, which was reflected in the President's speech.

But Yechury said there are two Indias in the making -- the IPL India and the BPL (below poverty line) India -- given the government's faulty and lopsided policies.

"The only deficit we talked about earlier was the fiscal deficit. Today, we have ethical deficit, moral deficit, governance deficit...Corruption cannot be fought without fighting the entire trajectory of your neo-liberal economic reforms,'' he said.

Demanding a course-correction, he said living conditions of the people had "abysmally deteriorated'' while multi-billion tax concessions -- worth Rs 2,25,000 crore in the last two years -- were being given to corporates and high-end tax payers.

If these tax concessions had been collected and invested in food security, right to education, health and infrastructure, they would have generated massive employment, demand and "real inclusive economic growth'', he said.

Referring to the 2G telecom scam, he said, "You have chosen not to tax the corporates but the scam lies in the fact that the licences were sold at least six times their value within six months.''

If the government had agreed for a JPC earlier, Parliament's winter session could have been saved. "We wanted a JPC to examine how our system could be so manipulated to allow such a big scam,'' he said.

Speaking after Yechury, Rajeev Shukla (Cong) urged the Opposition to restrain itself from painting an entirely negative image of the government, holding that it impacted foreign direct investment in the country.

Applauding the decision for a JPC probe into the 2G spectrum allocation, he said, "JPC probe should be 1990 onwards...if possible, probe should be done on disinvestments too....either by Arun Shourie or us.''

Dr Reddy's Phase III drug stumbles

The much-hyped anti-diabetic drug Balaglitazone of the pharma major Dr Reddy’s Laboratories (DRL) seems to be in trouble with the company not able to find a partner to take the discovery of the molecule forward.

“It is becoming difficult for us to find a partner for the drug research,” K Anji Reddy, DRL’s chairman, said.

Balaglitazone is a type-2 diabetic controller molecule, which is going through Phase-III trials. The Danish research company Rheoscience is already partnering with DRL for the drug development.

“Drug discovery is a high risk business where failure is more the norm than exception. We have to accept failures. Ten years of work has gone into flames,” Reddy said.

DRL has already announced that the drug met its primary endpoint of lowering blood sugar with few adverse events.

However, a similar compound was banned in Europe recently making it difficult for DRL to find a partner to take the research forward. This is said to have affected the progress of the research.

“We could not find partners for the drug,” Reddy said.

In 1997, Dr Reddy’s licensed Balaglitazone to Novo Nordisk. But in 2004, after Phase II studies, Novo Nordisk decided to terminate further clinical development of Balaglitazone as the Phase II results did not suggest a sufficient competitive advantage compared to the existing products.

Later the company entered into an agreement with Rheoscience for taking the research forward. However, the company in a statement on the status of the research said, “Additional clinical studies would depend on the breadth of the labelling sought feedback from the regulators. Dr Reddy’s and Rheoscience intend to seek an additional partner to complete the required phase III studies prior to approval. The strategy would be finalised with the

Cricket Cricket World Cup: Pakistan grapple with Sri Lanka M-factor

COLOMBO: Pakistan will look to blunt Lasith Malinga and wily off-spinner Muttiah Muralitharan in their Group A encounter against Sri Lanka on Saturday, with captain Shahid Afridi confident of a win.

Co-hosts Sri Lanka, champions in 1996, and 1992 winners Pakistan are off to flying starts in the tournament with convincing wins against minnows Canada and Kenya, and are primed for their first big match.

"I am confident that we are up to the Sri Lankan challenge and ready for anything they throw at us, whether its Malinga or Muralitharan," said Afridi.

Muralitharan, who has a world record 521 wickets in 342 one-day internationals, has a tally of 95 against Pakistan in 64 matches, and is even more dangerous in home conditions.

"In Sri Lankan conditions and pitches, he (Muralitharan) is always very dangerous and he could probably turn the ball on the marble as well. He has so much experience and knows conditions well and that's why he is the best," said Afridi.

Afridi said Malinga, renowned for his slingy action, would find it tough after missing the Canada match due to a back strain.

"Malinga is a very good bowler but he is coming back from an injury, so let's see how strong he is and how much he can adjust to the conditions," said Afridi.

Malinga has just ten wickets in nine matches against Pakistan including a best of 5-34.

Pakistan have also handled spinner Ajantha Mendis well. He has ten wickets against them in six matches.

Afridi hoped the sell-out match would be entertaining in a World Cup that needs a blockbuster clash between two of the big guns.

"It will be a good game. If we bowl well, bat well and go with positive body language and show more readiness for the game and willingness to win, I am sure we can pull it off," said Afridi.

Pakistan have never lost a World Cup match against Sri Lanka in six previous attempts but they were all before Sri Lanka became one of the top sides in the world game.

"The last match Sri Lanka played against us their fast bowlers did really well and they have a very good team combination. They've got good new guys in the side so we will have to play with our full strength and to win against them we need to give more than 100 percent effort," said Afridi.

Pakistan will look to improve on their starts -- both in batting and bowling -- at the match in Colombo.

"We are not short on motivation and our energy levels are good," said Afridi, looking to restrict the in-form Mahela Jayawardene, who scored a match-winning hundred during the team's 210-run win over Canada.

Besides Jayawardene, captain Kumar Sangakkara, Tillakaratne Dilshan and Upul Tharanga are in good form with the bat.

Jayawardene acknowledged Pakistan were a dangerous side.

"They (Pakistan) are a very good side, so we look forward to playing Pakistan. The boys showed great attitude in the match against Canada," said Jayawardene.

Sri Lanka will likely bring Malinga into the side in place of Thisara Perera, who took three wickets in the Canada match.

Pakistan will try to squeeze in off-spinner Saeed Ajmal, who has not played since his father's death in January this year. (AFP)

Bips, Deepika's fight over first look

It seems the title song of Rohan Sippy's Dum Maro Dum, an item number picturised on Deepika Padukone, has ruffled quite a few feathers.

First it was Dev Anand who raised an objection to how no one had contacted him about the rights of the song from his 1970s blockbuster Hare Rama Hare Krishna.

Then it was the Goan government itself that started getting tetchy about how the tropical paradise was being depicted (accurately, some could say, with Russian mafia and drugged out teens).

Now apparently Bipasha Basu, the leading lady of the film is stomping her foot; the item number, starring Deepika Padukone, is what is being perceived as the first look of the film. In fact the poster only has Deepika grooving to the number and no one else.

This is giving the impression that it is a Deepika starrer. Bips has been pipped! It needs to be reminded that Deepika and Bips also had a cold war when starring together in Bachna Ae Haseeno, starring poster boy Ranbir.

Our source from the production house said, "There were various debates about how the first look poster of the film will be made.

Finally it was decided that rather than having Abhishek Bachchan and Bipasha Basu on the posters of the film it would be nice to have Deepika who features in the item song `Dum Maro Dum'.

When Bipasha learnt about the poster she was not very happy and called Rohan Sippy who explained his promotional strategy to her."

When contacted Rohan Sippy said, "Deepika is doing a title song of the film. On the teaser poster you can hardly recognise Deepika.

It's brand Dum Maaro Dum and Bipasha is the female lead of the film. But I guess that's what happens with guest numbers and with iconic songs."

On the other hand, Bipasha denied any dispute and said, "I was the first one to tweet about the first look of DMD because I loved it and am super excited about our film.

Deepika is a super dancer and has done total justice to our song. There are no controversies here."

Apple May Unveil Updated IPad on March 2 in San Francisco

Apple Inc. , the world's biggest technology company by market value, may unveil its new iPad tablet computer at an event March 2 in San Francisco.

An Apple invitation sent to reporters today with the image of a corner of an iPad, says, "Come see what 2011 will be the year of." The event will be held at 10 a.m. local time.

The original iPad went on sale April 3, and Apple sold almost 15 million units through its first fiscal quarter , which ended Dec. 25. The device accounted for 17 percent of revenue in the period, compared with 39 percent for the iPhone, which first reached the market in 2007.

The timing of the March 2 event would put the iPad on an annual cycle of updates similar to those of the iPhone and iPod media player, and keep Apple ahead of competitors, said Scott Sutherland, an analyst at Wedbush Securities Inc. in San Francisco.

"The tablet becomes the next growth starter for the next two years for Apple," said Sutherland, who rates Apple shares "outperform" and doesn't own any. The company is releasing a second edition while many competitors are introducing their first tablets, he said.

Motorola Mobility Holdings Inc.'s Xoom tablet will be available tomorrow, and Research In Motion Ltd. plans to release four versions of its PlayBook this year.

Battery Life

Mike Abramsky , an analyst at RBC Capital Markets in Toronto, said in November that Apple may introduce a thinner iPad in the first half of 2011. Richard Doherty , director of consulting firm Envisioneering Group in Seaford, New York, said today he expects the updated iPad to offer longer battery life and front- and rear-facing cameras.

Apple is boosting its sales force to focus on burgeoning demand from business customers, particularly for the iPhone and iPad, Chief Operating Officer Tim Cook told a shareholders' meeting today.

"We've never seen anything like this before," Cook said.

Apple, based in Cupertino, California, rose $4.01 to $342.62 at 4 p.m. New York time in Nasdaq Stock Market trading. The shares have gained 6.2 percent this year.

Brent oil hits $113 on Libya unrest; Asian stocks off lows(business)

Unrest in Libya and the threat of contagion to other oil producing countries in the region drove Brent crude to USD 113 a barrel on Thursday, but the selloff in Asian stocks eased as investors started to nibble at beaten-down shares.

Copper also bounced off one-month lows, although the dollar stayed on the back foot as some investors worry that the US economy would be vulnerable to high oil prices, given its reliance on consumer spending to drive growth.

London Brent crude rose as high as USD 113 a barrel for the first time since September 2008, having gained nearly 10% in the past four sessions. US crude last traded at around USD 99.38 a barrel, a whisker away from Wednesday's high of USD 100.

Worries that higher energy prices will crimp corporate profits had sparked a steep selloff in Asian stocks in the past two sessions, but that looked to be losing its punch.

Japan's Nikkei 225 index, while still 0.4% lower on the day, was off its lows and stocks elsewhere in Asia erased early losses to be up 0.4%.

"As Japanese stocks have tumbled for the past two sessions (losing 2.6%), today's losses may not be sharp," said Masumi Yamamoto, a market analyst at Daiwa Securities Capital Markets.

Hong Kong's Hang Seng put on 0.2% and China's Shanghai Composite Index edged up 0.2%. Gains in US stock futures suggest a steadier start on Wall Street after two sessions of declines.

Gold , a traditional safe haven in times of trouble, traded at around USD 1,412 an ounce, not far from a record high around USD 1,430 set in December.

Copper gained 1.1% to USD 9,526 a tonne, climbing off a one-month low of USD 9,365.

The dollar index, which tracks its performance against a basket of major currencies, shed 0.3% to 77.173.

Against the Swiss franc, the dollar fell to a record low at around 0.9277 franc , surpassing the previous trough of 0.9301 set at the end of the year.

The euro held firm at USD 1.3776 , coming within easy reach of its February 2 peak of USD 1.3862, helped also by recent hawkish comments on inflation by European Central Bank officials, which raised expectations the ECB will hike interest rates before the Federal Reserve.

"There may be a realisation that if oil prices rise sharply, that would hit all the developed countries and in that sense it effects every major currency the same," said Tsutomu Soma, manager of foreign bonds at Okasan Securities.

"And if the impact from the Middle East crisis is roughly equal on each currency, you could argue that currencies with a yield advantage will benefit at the end of the day," Soma said.

The New Zealand dollar continued to struggle at two-month lows below USD 0.7500, with markets now pricing in an 88% chance that the next rate move will be a 25 basis point cut .

The move followed the deadly earthquake that hit the country's second biggest city of Christchurch on Tuesday.

Obama calls for unified global response on Libya

U.S. President Barack Obama on Thursday expressed outrage over the bloodshed in Libya and asked the world to speak in one voice against violence by the Qaddafi regime, as his administration evaluated a “range of options” to respond to the crisis.

As blood continued to spill on the streets of Libya for over a week, Mr. Obama, in his first remarks to the press over the crisis, sought to send out a tough message to the Libyan regime, indicating that strong unilateral and multilateral measures may be on their way to put it to accountability.

“In a volatile situation like this one, it is imperative that the nations and peoples of the world speak with one voice, and that has been our focus,” Mr. Obama said.

While Peru has already suspended diplomatic ties with Libya, Germany has sought sanctions against its regime.

Mr. Obama said the suffering and bloodshed is outrageous and unacceptable, and so were the threats being delivered by the regime to punish the people of Libya. “These actions violate international norms and every standard of common decency,” he said in a statement.

He pointed out that a unanimous United Nations Security Council on Tuesday had sent a clear message that it condemns the violence in Libya, supports accountability for the perpetrators, and stands with the Libyan people. This same message, he said, has been delivered by the European Union, the Arab League, the African Union, the Organisation of Islamic Conference and many individual nations.

“North and south, east and west, voices are being raised together to oppose suppression and support the rights of the Libyan people. I’ve also asked my administration to prepare the full range of options that we have to respond to this crisis. This includes those actions we may take and those we will coordinate with our allies and partners, or those that we’ll carry out through multilateral institutions,” he said.

The President said like all governments, the Libyan government has a responsibility to refrain from violence, to allow humanitarian assistance to reach those in need, and to respect the rights of its people.

“It must be held accountable for its failure to meet those responsibilities, and face the cost of continued violations of human rights. This is not simply a concern of the United States. The entire world is watching, and we will coordinate our assistance and accountability measures with the international community,” he said.

The Libyan Interior Ministry has put the death toll in over a week of violence at 300, but Italian Foreign Minister Franco Frattini claimed that the crackdown has killed as many as 1,000 people.

Reports have said that a number of cities have slipped off government control and were now being held by the people.

Maoists set new conditions more for Orissa collector's release(news)

Within hours of releasing the abducted junior engineer after days of negotiations with the Orissa government, Maoist rebels on Wednesday put forward new conditions for the release of Malkangiri district collector R Vineel Krishna. Junior engineer Pabitra Mohan Majhi was released on Wednesday af
related stories

* Engineer released, collector may be free soon
* Fast track court grants bail to hardcore Maoist

ternoon as per the agreement reached by the government during the negotiations with mediators, chosen by rebels.

The release came after the government gave in to nearly 14 demands of the Leftist rebels including release of their jailed comrades.

But in a dramatic turnaround, by late Wednesday the rebels put new conditions for the release of their biggest catch to date -- the young Indian Administrative Service officer Krishna.

The turnaround stumped the mediators too.

In a press conference late Wednesday, the mediators said that they are surprised with the development and the fresh demands made by the rebels are not acceptable to them.

"For the release of the district collector they have set certain conditions," said G Haragopal, an academician and one of the three mediators of the hostage crisis.

"It will not be possible for us to abide by these conditions," he said. Without detailing the new terms set by the rebels, he said, "We have a feeling that this will complicate the matter."

Dandapani Mohanty, another mediator, was a little more forthcoming on the demands. "They want the mediators to visit Malkangiri district. The new conditions are not acceptable to us. We appeal to them to release the collector as per the deadline of 48 hours (Thursday evening)."

Earlier in the day, junior engineer Majhi said the kidnapped collector was safe and the rebels will free him within 48 hours.

People across the state were glued to television sets, awaiting the news of Krishna's release.

"He (collector) is safe and is still in the cut-off area. I do not know the exact location. The Maoists said they will release him within 48 hours," Majhi said at a press conference in the district headquarter town of Malkangiri, about 618 km from here.

"They fed us rice and dal and we were being moved from one place to another" during the week-long captivity, he said. Majhi also said that the rebels did not cause any mental or physical harm to them.

Replying to a question about reports that the collector was ill and refused food, Majhi said, "He was in good health and was eating fine."

Majhi was released in the same Chitrakonda area, about 700 km from Bhubaneswar, from where he was kidnapped along with Collector Krishna on Feb 16, sending shock waves across the country.

"We don't have any information so far about the release of the collector," a senior state police officer said.

The state government and people from various walks of life, including women, children and media persons, anxiously watched television sets for the latest updates. Thousands of people also rushed to the collector's official residence.

Curiously, a top Maoist leader who was granted bail as part of the mediation process refused to leave prison, negotiators said.

Wednesday saw the state high court grant bail to Maoist ideologue Ganti Prasadam - one of the seven top rebels whose release was sought in exchange for the freedom of the abducted officials. But Prasadam refused to leave prison, negotiators said.

"Until and unless the government takes steps for the release of over 600 innocent people languishing in various jails on the charge of being involved in Maoist activities, Prasadam says he will not leave prison," said Mohanty.

Orissa Police, on a prison transfer granted by a court, brought Prasadam from a jail in Andhra Pradesh on Saturday night after the mediators sought his presence to speed up the negotiations that started Sunday.

Prasadam is facing several charges in Andhra Pradesh and Orissa. His bail petition was moved Monday in the Orissa High Court in Cuttack, 26 km from here, after it was rejected by a lower court.

The Maoists had set 14 conditions, including the halt to anti-Maoist operations, release of all political prisoners, and scrapping of accords with multi-national companies for land transfer and projects in Orissa.

The government agreed to all the demands after holding negotiations here with the three mediators - Mohanty and Haragopal and R Someswar Rao.

joke1

Ragging k waqt ladko ne
ek ladki se kaha ,
Ek – sawal ka jawab
Do – Patna kahan hai ?
Ladki – Bihar me .
Boys – yahi pat jao itni dur jaane ki kya zarurat hai .

Wife – kitchen se aji sunte ho
aajkal mai khubsurat hoti ja rahi hue .
Husband – : tumne kaise jana
Wife :- aaj kal meri khubsurti dekhkar rotiyan bhi jalne lagi hai …..

joke

kya meri nak tedi hai. ankhen mendki jesi hai. surat se besharm lagta hoon, pagal hoon akal nahi mujhe… phir kise ne aisa kiyo kaha meri surat tumse milte hai………….?

yr 1 : janu
yr 2 : O ji
yr 3 : sunte ho?
yr 4 : O bunty ke papa
yr 5 : kide mar gaye?

TUSI bade hi gr8 ho,
RASGULLE ki pl8 ho,
PEPSI ka cr8 ho,
ANDE ka oml8 ho,
SMS KARANE ME bade le8 ho,
JALEBI ki tarah stra8 ho,
KHER jo bhi ho mere fevr8 ho…!

Lamhe judai ke bekarar karte hain,
Haalat meri mujhe laachar karte hain,
Aankhe meri pad lo kabhi,
Ham khud kaise kahe ki
hum aapse pyaar karte hain.

Tere liye agar jan vi dene pade
kurban he jan tujhpar khuda sevi na darte he hum
tumare hawas vari nigaye kaise janegi ye raj
ke duniya me sabse bada pyar tumhiko karte he hum.

Nanded Historical importance

anded is one of the historical places in Marathwada region of Maharashtra State. It is situated on the north bank of Godavari river. It is famous for Sikh Gurudwaras. Nanded is a town of great antiquity. It is said that during the Puranic days, Pandavas travelled through Nanded district. Nandas ruled over Nanded through generations.

The mention of Nanded is found in the Lilacharitra, a treatise written by Mahimbhatta. It gives the description of the idol of Narasimha in the town. Nanded was formerly known as "Nanditat" which is confirmed by the copper plate found at Vasim. Nanded District and the adjoining areas were ruled over by the Andhrabhrtyas or Satvahanas during the First Centrury A.D. During the fourth century A.D. Kandhar was the capital of the King Sogadev and at Nanded was ruled by the king Nanddeva of the Chalukya dynasty. That the Rashtrakutas were ruling at Kandhar is established by the inscription at Krishnadev alias Khandardev found at Khandar. Another inscription at Ardhapur shows that some dynasty of the Rashtrakutas was also ruling over Degloor. Hottal, a place in Nanded District was the capital of the Chalukyas, Kakatiyas followed by the Yadavas of Devgiri were the last Hindu dynasties to have ruled of this part. During the very first invasion by Muhammedans this territory subjugated to them and after a few years it became a part of the fief of Malik kafur, the general of Alauddin Khilji.

With the advent of the Bahamanis, the southern country or the Deccan was divided into four parts or the subhas and Nanded was included in the Subha of Telangana. The famous Vazir or the Prime Minister of the Bahamanis Mahmud Gavan divided the Kingdom into subhas with Nanded forming part of Mahur Balaghat. Resided at Nanded and Kandhar for many days and the Vazirabad part of Nanded town was established, While he was residing at Nanded and Kandhar.

When Aurangzeb was appointed the Subhedar of the Deccan. Bidar was one of the Subha. The Subha of Bidar was divided into six sarkars and 76 mahals and Nanded was one of the Sarkars of that subha.

In 1708, the year following the death of Aurangzeb, his son accompained by Guru Govind Singh the tenth spiritual leader of the Sikhs came over to Nanded, as his permanent abode. It was he who preached amongst the sikhs that there need not be any spiritual leader for them and they should take Granthsaheb as their leader. A monument has been constructed at place where he breathed his last. A Gurudwara has also been constructed there and is known as Shri Hazur Abchalnagar Sachkhand Gurudwara.

It became the part of the Hyderabad Kingdom in 1725 when the Nizam permanently opted for the Deccan and continued to be so till 1947. With India getting freedom and the consequent police action against the Hyderabad State, the district forming part of the Marathwada region of the Hyderabad state became part of the bilingual Bombay State and consequent upon the creation of Maharashtra, the district continues to form part of the state of Maharashtra.

Nanded has a great cultural heritage. It is the place of birth of the Saint poets like Vishnupant Sesa and Raguhunath Sesa and Vaman Pandit besides being a Centre for learning Sanskrit.

Indian Education

Indian Department of Education


Ministry of Human Resource Development
Kapil Sibal


National education budget (2010)



Budget:
31,036 crore (US$6.73 billion) (2009-10)


General Details



Primary Languages:
Hindi, English, or State language


System Type:
Federal, state, private



Literacy (2001^[1])


Total:
66%


Male:

76.9%


Female:
54.5%


Enrollment ((N/A))


Total:

(N/A)


Primary:
(N/A)


Secondary:
(N/A)


Post Secondary:

(N/A)


Attainment


Secondary diploma
15%


Post-secondary diploma

7%


v · d · e

Motherboard

From Wikipedia, the free encyclopedia

Jump to: navigation,
search

In personal computers, a motherboard is the central printed circuit board (PCB) in many modern computers and holds many of the crucial components of the system, while providing connectors for other peripherals. The motherboard is sometimes alternatively known as the main board, system board, or, on Apple computers, the logic board.^[1] It is also sometimes casually shortened to mobo.^[2]

A motherboard for a desktop personal computer

Contents [hide] 1 History 2 Overview 2.1 CPU sockets 2.2 Integrated peripherals 2.3 Peripheral card slots 2.4 Temperature and reliability 2.5 Form factor 3 Bootstrapping using the BIOS 4 See also 5 References 6 External links

[edit] History

Prior to the advent of the microprocessor, a computer was usually built in a card-cage case or mainframe with components connected by a backplane consisting of a set of slots themselves connected with wires; in very old designs the wires were discrete connections between card connector pins, but printed circuit boards soon became the standard practice. The Central Processing Unit, memory and peripherals were housed on individual printed circuit boards which plugged into the backplane.

During the late 1980s and 1990s, it became economical to move an increasing number of peripheral functions onto the motherboard (see below). In the late 1980s, motherboards began to include single ICs (called Super I/O chips) capable of supporting a set of low-speed peripherals: keyboard, mouse, floppy disk drive, serial ports, and parallel ports. As of the late 1990s, many personal computer motherboards supported a full range of audio, video, storage, and networking functions without the need for any expansion cards at all; higher-end systems for 3D gaming and computer graphics typically retained only the graphics card as a separate component.

The early pioneers of motherboard manufacturing were Micronics, Mylex, AMI, DTK, Hauppauge, Orchid Technology, Elitegroup, DFI, and a number of Taiwan-based manufacturers.

The most popular computers such as the Apple II and IBM PC had published schematic diagrams and other documentation which permitted rapid reverse-engineering and third-party replacement motherboards. Usually intended for building new computers compatible with the exemplars, many motherboards offered additional performance or other features and were used to upgrade the manufacturer's original equipment.

The term mainboard is applied to devices with a single board and no additional expansions or capability. In modern terms this would include embedded systems and controlling boards in televisions, washing machines, etc. A motherboard specifically refers to a printed circuit board with expansion capability.

[edit] Overview

A motherboard, like a backplane, provides the electrical connections by which the other components of the system communicate, but unlike a backplane, it also connects the central processing unit and hosts other subsystems and devices.

A typical desktop computer has its microprocessor, main memory, and other essential components connected to the motherboard. Other components such as external storage, controllers for video display and sound, and peripheral devices may be attached to the motherboard as plug-in cards or via cables, although in modern computers it is increasingly common to integrate some of these peripherals into the motherboard itself.

An important component of a motherboard is the microprocessor's supporting chipset, which provides the supporting interfaces between the CPU and the various buses and external components. This chipset determines, to an extent, the features and capabilities of the motherboard.

Modern motherboards include, at a minimum:

• sockets (or slots) in which one or more microprocessors may be installed^[3]



• slots into which the system's main memory is to be installed (typically in the form of DIMM modules containing DRAM chips)


• a chipset which forms an interface between the CPU's front-side bus, main memory, and peripheral buses


• non-volatile memory chips (usually Flash ROM in modern motherboards) containing the system's firmware or BIOS



• a clock generator which produces the system clock signal to synchronize the various components


• slots for expansion cards (these interface to the system via the buses supported by the chipset)


• power connectors, which receive electrical power from the computer power supply and distribute it to the CPU, chipset, main memory, and expansion cards.^[4]

The Octek Jaguar V motherboard from 1993.^[5] This board has 6 ISA slots but few onboard peripherals, as evidenced by the lack of external connectors.

Additionally, nearly all motherboards include logic and connectors to support commonly used input devices, such as PS/2 connectors for a mouse and keyboard. Early personal computers such as the Apple II or IBM PC included only this minimal peripheral support on the motherboard. Occasionally video interface hardware was also integrated into the motherboard; for example, on the Apple II and rarely on IBM-compatible computers such as the IBM PC Jr. Additional peripherals such as disk controllers and serial ports were provided as expansion cards.

Given the high thermal design power of high-speed computer CPUs and components, modern motherboards nearly always include heat sinks and mounting points for fans to dissipate excess heat.

[edit] CPU sockets

Main article: CPU socket

A CPU socket or slot is an electrical component that attaches to a printed circuit board (PCB) and is designed to house a CPU (also called a microprocessor). It is a special type of integrated circuit socket designed for very high pin counts. A CPU socket provides many functions, including a physical structure to support the CPU, support for a heat sink, facilitating replacement (as well as reducing cost), and most importantly, forming an electrical interface both with the CPU and the PCB. CPU sockets can most often be found in most desktop and server computers (laptops typically use surface mount CPUs), particularly those based on the Intel x86 architecture on the motherboard. A CPU socket type and motherboard chipset must support the CPU series and speed.

[edit] Integrated peripherals

Block diagram of a modern motherboard, which supports many on-board peripheral functions as well as several expansion slots.

With the steadily declining costs and size of integrated circuits, it is now possible to include support for many peripherals on the motherboard. By combining many functions on one PCB, the physical size and total cost of the system may be reduced; highly integrated motherboards are thus especially popular in small form factor and budget computers.

For example, the ECS RS485M-M,^[6] a typical modern budget motherboard for computers based on AMD processors, has on-board support for a very large range of peripherals:

• disk controllers for a floppy disk drive, up to 2 PATA drives, and up to 6 SATA drives (including RAID 0/1 support)



• integrated graphics controller supporting 2D and 3D graphics, with VGA and TV output


• integrated sound card supporting 8-channel (7.1) audio and S/PDIF output



• Fast Ethernet network controller for 10/100 Mbit networking


• USB 2.0 controller supporting up to 12 USB ports


• IrDA controller for infrared data communication (e.g. with an IrDA-enabled cellular phone or printer)



• temperature, voltage, and fan-speed sensors that allow software to monitor the health of computer components

Expansion cards to support all of these functions would have cost hundreds of dollars even a decade ago; however, as of April 2007^[update] such highly integrated motherboards are available for as little as $30 in the USA.

[edit] Peripheral card slots

A typical motherboard of 2009 will have a different number of connections depending on its standard.

A standard ATX motherboard will typically have one PCI-E 16x connection for a graphics card, two conventional PCI slots for various expansion cards, and one PCI-E 1x (which will eventually supersede PCI). A standard EATX motherboard will have one PCI-E 16x connection for a graphics card, and a varying number of PCI and PCI-E 1x slots. It can sometimes also have a PCI-E 4x slot. (This varies between brands and models.)

Some motherboards have two PCI-E 16x slots, to allow more than 2 monitors without special hardware, or use a special graphics technology called SLI (for Nvidia) and Crossfire (for ATI). These allow 2 graphics cards to be linked together, to allow better performance in intensive graphical computing tasks, such as gaming and video editing.

As of 2007, virtually all motherboards come with at least four USB ports on the rear, with at least 2 connections on the board internally for wiring additional front ports that may be built into the computer's case. Ethernet is also included. This is a standard networking cable for connecting the computer to a network or a modem. A sound chip is always included on the motherboard, to allow sound output without the need for any extra components. This allows computers to be far more multimedia-based than before. Some motherboards have their graphics chip built into the motherboard rather than needing a separate card. A separate card may still be used.

[edit] Temperature and reliability

Main article: Computer cooling

Motherboards are generally air cooled with heat sinks often mounted on larger chips, such as the Northbridge, in modern motherboards. If the motherboard is not cooled properly, it can cause the computer to crash. Passive cooling, or a single fan mounted on the power supply, was sufficient for many desktop computer CPUs until the late 1990s; since then, most have required CPU fans mounted on their heat sinks, due to rising clock speeds and power consumption. Most motherboards have connectors for additional case fans as well. Newer motherboards have integrated temperature sensors to detect motherboard and CPU temperatures, and controllable fan connectors which the BIOS or operating system can use to regulate fan speed. Some computers (which typically have high-performance microprocessors, large amounts of RAM, and high-performance video cards) use a water-cooling system instead of many fans.

Some small form factor computers and home theater PCs designed for quiet and energy-efficient operation boast fan-less designs. This typically requires the use of a low-power CPU, as well as careful layout of the motherboard and other components to allow for heat sink placement.

A 2003 study^[7] found that some spurious computer crashes and general reliability issues, ranging from screen image distortions to I/O read/write errors, can be attributed not to software or peripheral hardware but to aging capacitors on PC motherboards. Ultimately this was shown to be the result of a faulty electrolyte formulation.^[8]

For more information on premature capacitor failure on PC motherboards, see capacitor plague.

Motherboards use electrolytic capacitors to filter the DC power distributed around the board. These capacitors age at a temperature-dependent rate, as their water based electrolytes slowly evaporate. This can lead to loss of capacitance and subsequent motherboard malfunctions due to voltage instabilities. While most capacitors are rated for 2000 hours of operation at 105 °C,^[9] their expected design life roughly doubles for every 10 °C below this. At 45 °C a lifetime of 15 years can be expected. This appears reasonable for a computer motherboard. However, many manufacturers have delivered substandard capacitors,^{[citation needed]} which significantly reduce life expectancy. Inadequate case cooling and elevated temperatures easily exacerbate this problem. It is possible, but tedious and time-consuming, to find and replace failed capacitors on PC motherboards.

[edit] Form factor

Main article: Comparison of computer form factors

microATX form factor motherboard

Motherboards are produced in a variety of sizes and shapes called computer form factor, some of which are specific to individual computer manufacturers. However, the motherboards used in IBM-compatible to fit various case sizes. As of 2007^[update], most desktop computer motherboards use one of these standard form factors—even those found in Macintosh and Sun computers, which have not traditionally been built from commodity components. The current desktop PC form factor of choice is ATX. A case's motherboard and PSU form factor must all match, though some smaller form factor motherboards of the same family will fit larger cases. For example, an ATX case will usually accommodate a microATX motherboard.

Laptop computers generally use highly integrated, miniaturized and customized motherboards. This is one of the reasons that laptop computers are difficult to upgrade and expensive to repair. Often the failure of one laptop component requires the replacement of the entire motherboard, which is usually more expensive than a desktop motherboard due to the large number of integrated components.

[edit] Bootstrapping using the BIOS

Main article: booting

Motherboards contain some non-volatile memory to initialize the system and load an operating system from some external peripheral device. Microcomputers such as the Apple II and IBM PC used ROM chips, mounted in sockets on the motherboard. At power-up, the central processor would load its program counter with the address of the boot ROM and start executing ROM instructions, displaying system information on the screen and running memory checks, which would in turn start loading memory from an external or peripheral device (disk drive). If none is available, then the computer can perform tasks from other memory stores or display an error message, depending on the model and design of the computer and version of the BIOS.

Most modern motherboard designs use a BIOS, stored in an EEPROM chip soldered or socketed to the motherboard, to bootstrap an operating system. When power is first applied to the motherboard, the BIOS firmware tests and configures memory, circuitry, and peripherals. This Power-On Self Test (POST) may include testing some of the following devices:

• video adapter



• cards inserted into slots, such as conventional PCI


• floppy drive


• thermistors, voltages, and fan speeds for hardware monitoring


• CMOS used to store BIOS setup configuration



• keyboard and mouse


• network controller


• optical drives: CD-ROM or DVD-ROM


• SCSI hard drive



• IDE, EIDE, or SATA hard disk


• security devices, such as a fingerprint reader or the state of a latch switch to detect intrusion


• USB devices, such as a memory storage device

On recent motherboards, the BIOS may also patch the central processor microcode if the BIOS detects that the installed CPU is one in for which errata has been published. Many of the above devices can be stored with machine code instructions to load an operating system or program.

[edit] See also

• Accelerated Graphics Port (AGP)


• Backplane


• BIOS


• Central Processing Unit


• Chipset


• Computer case


• Conventional PCI



• Daughterboard


• Front-side bus


• Industry Standard Architecture (ISA)*List of motherboard manufacturers


• Offboard


• Overclocking


• PCI Express


• Single-board computer

[edit] References

1. ^ Paul Miller. "Apple sneaks new logic board into whining MacBook Pros" (2006). Engadget. http://www.engadget.com/2006/07/08/apple-sneaks-new-logic-board-into-whining-macbook-pros/. Retrieved 2008-10-23. 



2. ^ "mobo". Webopedia. http://www.webopedia.com/TERM/M/mobo.html. Retrieved 2008-10-23. 


3. ^ In the case of CPUs in BGA packages, such as the VIA C3, the CPU is directly soldered to the motherboard.



4. ^ As of 2007^[update], some graphics cards (e.g. GeForce 8 and Radeon R600) require more power than the motherboard can provide, and thus dedicated connectors have been introduced to attach them directly to the power supply. (Note that most disk drives also connect to the power supply via dedicated connectors.)



5. ^ "Golden Oldies: 1993 mainboards". http://redhill.net.au/b/b-93.html. Retrieved 2007-06-27. 


6. ^ "RS485M-M (V1.0)". http://www.ecs.com.tw/ECSWebSite/Products/ProductsDetail.aspx?DetailID=654&CategoryID=1&DetailName=Feature&MenuID=46&LanID=9. Retrieved 2007-06-27. 



7. ^ c't Magazine, vol. 21, pp. 216-221. 2003.


8. ^ Yu-Tzu Chiu, Samuel K. Moore "Faults & Failures: Leaking Capacitors Muck up Motherboards" (2003-02-19) IEEE Spectrum accessed 2008-03-10



9. ^ See the capacitor lifetime formula at [1].

[edit] External links

Wikimedia Commons has media related to: Computer motherboards

• List of motherboard manufacturers and links to BIOS updates


• What is a motherboard?


• The Making of a Motherboard: ECS Factory Tour


• The Making of a Motherboard: Gigabyte Factory Tour


• Motherboard reviews



• Motherboards at the Open Directory Project


• Front Panel I/O Connectivity Design Guide - v1.3 (pdf file) (February 2005)

[hide]v · d · eBasic computer components Input devices Keyboard · Pointing device (Joystick · Light pen · Mouse · Touchpad · Touchscreen · Trackball) · Microphone · Scanner · Webcam Output devices Monitor  · Speakers  · Printer Removable data storage Floppy disk · Compact Disc ReWritable / DVD Drive  · USB flash drive · Memory card Computer case Central processing unit · RAM · Video card · Sound card · Motherboard · Power supply · Hard drive · Network interface controller Data ports Ethernet · Firewire (IEEE 1394) · Parallel port · Serial port · Universal Serial Bus (USB)

Retrieved from "http://en.wikipedia.org/wiki/Motherboard"

Categories: IBM PC compatibles | Motherboard

Hidden categories: Articles containing potentially dated statements from 2007 | All articles containing potentially dated statements | Articles containing potentially dated statements from April 2007 | All articles with unsourced statements | Articles with unsourced statements from September 2008

From Wikipedia, the free encyclopedia

Jump to: navigation,
search

For other uses, see Computer (disambiguation).

"Computer technology" redirects here. For the company, see Computer Technology Limited.

Computer

A computer is a programmable machine that receives input, stores and automatically manipulates data, and provides output in a useful format.

The first electronic computers were developed in the mid-20th century (1940–1945). Originally, they were the size of a large room, consuming as much power as several hundred modern personal computers (PCs).^[1]

Modern computers based on integrated circuits are millions to billions of times more capable than the early machines, and occupy a fraction of the space.^[2] Simple computers are small enough to fit into mobile devices, and can be powered by a small battery. Personal computers in their various forms are icons of the Information Age and are what most people think of as "computers". However, the embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are the most numerous.

Contents [hide] 1 History of computing 1.1 Limited-function ancient computers 1.2 First general-purpose computers 1.3 Stored-program architecture 1.4 Semiconductors and microprocessors 2 Programs 2.1 Stored program architecture 2.2 Bugs 2.3 Machine code 2.4 Higher-level languages and program design 3 Function 3.1 Control unit 3.2 Arithmetic/logic unit (ALU) 3.3 Memory 3.4 Input/output (I/O) 3.5 Multitasking 3.6 Multiprocessing 3.7 Networking and the Internet 4 Misconceptions 4.1 Required technology 4.2 Computer architecture paradigms 4.3 Limited-function computers 4.4 Virtual computers 5 Further topics 5.1 Artificial intelligence 5.2 Hardware 5.3 Software 5.4 Programming languages 5.5 Professions and organizations 6 See also 7 Notes 8 References 9 External links

History of computing

Main article: History of computing hardware

The first use of the word "computer" was recorded in 1613, referring to a person who carried out calculations, or computations, and the word continued with the same meaning until the middle of the 20th century. From the end of the 19th century onwards, the word began to take on its more familiar meaning, describing a machine that carries out computations.^[3]

Limited-function ancient computers

The Jacquard loom, on display at the Museum of Science and Industry in Manchester, England, was one of the first programmable devices.

The history of the modern computer begins with two separate technologies—automated calculation and programmability—but no single device can be identified as the earliest computer, partly because of the inconsistent application of that term. Examples of early mechanical calculating devices include the abacus, the slide rule and arguably the astrolabe and the Antikythera mechanism, an ancient astronomical computer built by the Greeks around 80 BC.^[4] The Greek mathematician Hero of Alexandria (c. 10–70 AD) built a mechanical theater which performed a play lasting 10 minutes and was operated by a complex system of ropes and drums that might be considered to be a means of deciding which parts of the mechanism performed which actions and when.^[5] This is the essence of programmability.

The "castle clock", an astronomical clock invented by Al-Jazari in 1206, is considered to be the earliest programmable analog computer.^{[6][verification needed]} It displayed the zodiac, the solar and lunar orbits, a crescent moon-shaped pointer travelling across a gateway causing automatic doors to open every hour,^[7][8] and five robotic musicians who played music when struck by levers operated by a camshaft attached to a water wheel. The length of day and night could be re-programmed to compensate for the changing lengths of day and night throughout the year.^[6]

The Renaissance saw a re-invigoration of European mathematics and engineering. Wilhelm Schickard's 1623 device was the first of a number of mechanical calculators constructed by European engineers, but none fit the modern definition of a computer, because they could not be programmed.

First general-purpose computers

In 1801, Joseph Marie Jacquard made an improvement to the textile loom by introducing a series of punched paper cards as a template which allowed his loom to weave intricate patterns automatically. The resulting Jacquard loom was an important step in the development of computers because the use of punched cards to define woven patterns can be viewed as an early, albeit limited, form of programmability.

The Most Famous Image in the Early History of Computing^[9]

This portrait of Jacquard was woven in silk on a Jacquard loom and required 24,000 punched cards to create (1839). It was only produced to order. Charles Babbage owned one of these portraits ; it inspired him in using perforated cards in his analytical engine^[10]

It was the fusion of automatic calculation with programmability that produced the first recognizable computers. In 1837, Charles Babbage was the first to conceptualize and design a fully programmable mechanical computer, his analytical engine.^[11] Limited finances and Babbage's inability to resist tinkering with the design meant that the device was never completed ; nevertheless his son, Henry Babbage, completed a simplified version of the analytical engine's computing unit (the mill) in 1888. He gave a successful demonstration of its use in computing tables in 1906. This machine was given to the Science museum in South Kensington in 1910.

In the late 1880s, Herman Hollerith invented the recording of data on a machine readable medium. Prior uses of machine readable media, above, had been for control, not data. "After some initial trials with paper tape, he settled on punched cards ..."^[12] To process these punched cards he invented the tabulator, and the keypunch machines. These three inventions were the foundation of the modern information processing industry. Large-scale automated data processing of punched cards was performed for the 1890 United States Census by Hollerith's company, which later became the core of IBM. By the end of the 19th century a number of technologies that would later prove useful in the realization of practical computers had begun to appear: the punched card, Boolean algebra, the vacuum tube (thermionic valve) and the teleprinter.

During the first half of the 20th century, many scientific computing needs were met by increasingly sophisticated analog computers, which used a direct mechanical or electrical model of the problem as a basis for computation. However, these were not programmable and generally lacked the versatility and accuracy of modern digital computers.

Alan Turing is widely regarded to be the father of modern computer science. In 1936 Turing provided an influential formalisation of the concept of the algorithm and computation with the Turing machine, providing a blueprint for the electronic digital computer.^[13] Of his role in the creation of the modern computer, Time magazine in naming Turing one of the 100 most influential people of the 20th century, states: "The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine".^[13]

The Zuse Z3, 1941, considered the world's first working programmable, fully automatic computing machine.

The ENIAC, which became operational in 1946, is considered to be the first general-purpose electronic computer.

EDSAC was one of the first computers to implement the stored program (von Neumann) architecture.

Die of an Intel 80486DX2 microprocessor (actual size: 12×6.75 mm) in its packaging.

The Atanasoff–Berry Computer (ABC) was among the first electronic digital binary computing devices. Conceived in 1937 by Iowa State College physics professor John Atanasoff, and built with the assistance of graduate student Clifford Berry,^[14] the machine was not programmable, being designed only to solve systems of linear equations. The computer did employ parallel computation. A 1973 court ruling in a patent dispute found that the patent for the 1946 ENIAC computer derived from the Atanasoff–Berry Computer.

The inventor of the program-controlled computer was Konrad Zuse, who built the first working computer in 1941 and later in 1955 the first computer based on magnetic storage.^[15]

George Stibitz is internationally recognized as a father of the modern digital computer. While working at Bell Labs in November 1937, Stibitz invented and built a relay-based calculator he dubbed the "Model K" (for "kitchen table", on which he had assembled it), which was the first to use binary circuits to perform an arithmetic operation. Later models added greater sophistication including complex arithmetic and programmability.^[16]

A succession of steadily more powerful and flexible computing devices were constructed in the 1930s and 1940s, gradually adding the key features that are seen in modern computers. The use of digital electronics (largely invented by Claude Shannon in 1937) and more flexible programmability were vitally important steps, but defining one point along this road as "the first digital electronic computer" is difficult.^{Shannon 1940} Notable achievements include.

• Konrad Zuse's electromechanical "Z machines". The Z3 (1941) was the first working machine featuring binary arithmetic, including floating point arithmetic and a measure of programmability. In 1998 the Z3 was proved to be Turing complete, therefore being the world's first operational computer.^[17]



• The non-programmable Atanasoff–Berry Computer (commenced in 1937, completed in 1941) which used vacuum tube based computation, binary numbers, and regenerative capacitor memory. The use of regenerative memory allowed it to be much more compact than its peers (being approximately the size of a large desk or workbench), since intermediate results could be stored and then fed back into the same set of computation elements.


• The secret British Colossus computers (1943),^[18] which had limited programmability but demonstrated that a device using thousands of tubes could be reasonably reliable and electronically reprogrammable. It was used for breaking German wartime codes.



• The Harvard Mark I (1944), a large-scale electromechanical computer with limited programmability.^[19]


• The U.S. Army's Ballistic Research Laboratory ENIAC (1946), which used decimal arithmetic and is sometimes called the first general purpose electronic computer (since Konrad Zuse's Z3 of 1941 used electromagnets instead of electronics). Initially, however, ENIAC had an inflexible architecture which essentially required rewiring to change its programming.

Stored-program architecture

Several developers of ENIAC, recognizing its flaws, came up with a far more flexible and elegant design, which came to be known as the "stored program architecture" or von Neumann architecture. This design was first formally described by John von Neumann in the paper First Draft of a Report on the EDVAC, distributed in 1945. A number of projects to develop computers based on the stored-program architecture commenced around this time, the first of these being completed in Great Britain. The first working prototype to be demonstrated was the Manchester Small-Scale Experimental Machine (SSEM or "Baby") in 1948. The Electronic Delay Storage Automatic Calculator (EDSAC), completed a year after the SSEM at Cambridge University, was the first practical, non-experimental implementation of the stored program design and was put to use immediately for research work at the university. Shortly thereafter, the machine originally described by von Neumann's paper—EDVAC—was completed but did not see full-time use for an additional two years.

Nearly all modern computers implement some form of the stored-program architecture, making it the single trait by which the word "computer" is now defined. While the technologies used in computers have changed dramatically since the first electronic, general-purpose computers of the 1940s, most still use the von Neumann architecture.

Beginning in the 1950s, Soviet scientists Sergei Sobolev and Nikolay Brusentsov conducted research on ternary computers, devices that operated on a base three numbering system of −1, 0, and 1 rather than the conventional binary numbering system upon which most computers are based. They designed the Setun, a functional ternary computer, at Moscow State University. The device was put into limited production in the Soviet Union, but supplanted by the more common binary architecture.

Semiconductors and microprocessors

Computers using vacuum tubes as their electronic elements were in use throughout the 1950s, but by the 1960s had been largely replaced by transistor-based machines, which were smaller, faster, cheaper to produce, required less power, and were more reliable. The first transistorised computer was demonstrated at the University of Manchester in 1953.^[20] In the 1970s, integrated circuit technology and the subsequent creation of microprocessors, such as the Intel 4004, further decreased size and cost and further increased speed and reliability of computers. By the late 1970s, many products such as video recorders contained dedicated computers called microcontrollers, and they started to appear as a replacement to mechanical controls in domestic appliances such as washing machines. The 1980s witnessed home computers and the now ubiquitous personal computer. With the evolution of the Internet, personal computers are becoming as common as the television and the telephone in the household^{[citation needed]}.

Modern smartphones are fully programmable computers in their own right, and as of 2009 may well be the most common form of such computers in existence^{[citation needed]}.

Programs

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that some type of instructions (the program) can be given to the computer, and it will carry process them. While some computers may have strange concepts "instructions" and "output" (see quantum computing), modern computers based on the von Neumann architecture are often have machine code in the form of an imperative programming language.

In practical terms, a computer program may be just a few instructions or extend to many millions of instructions, as do the programs for word processors and web browsers for example. A typical modern computer can execute billions of instructions per second (gigaflops) and rarely makes a mistake over many years of operation. Large computer programs consisting of several million instructions may take teams of programmers years to write, and due to the complexity of the task almost certainly contain errors.

Stored program architecture

Main articles: Computer program and Computer programming

A 1970s punched card containing one line from a FORTRAN program. The card reads: "Z(1) = Y + W(1)" and is labelled "PROJ039" for identification purposes.

This section applies to most common RAM machine-based computers.

In most cases, computer instructions are simple: add one number to another, move some data from one location to another, send a message to some external device, etc. These instructions are read from the computer's memory and are generally carried out (executed) in the order they were given. However, there are usually specialized instructions to tell the computer to jump ahead or backwards to some other place in the program and to carry on executing from there. These are called "jump" instructions (or branches). Furthermore, jump instructions may be made to happen conditionally so that different sequences of instructions may be used depending on the result of some previous calculation or some external event. Many computers directly support subroutines by providing a type of jump that "remembers" the location it jumped from and another instruction to return to the instruction following that jump instruction.

Program execution might be likened to reading a book. While a person will normally read each word and line in sequence, they may at times jump back to an earlier place in the text or skip sections that are not of interest. Similarly, a computer may sometimes go back and repeat the instructions in some section of the program over and over again until some internal condition is met. This is called the flow of control within the program and it is what allows the computer to perform tasks repeatedly without human intervention.

Comparatively, a person using a pocket calculator can perform a basic arithmetic operation such as adding two numbers with just a few button presses. But to add together all of the numbers from 1 to 1,000 would take thousands of button presses and a lot of time—with a near certainty of making a mistake. On the other hand, a computer may be programmed to do this with just a few simple instructions. For example:

      mov #0, sum     ; set sum to 0
      mov #1, num     ; set num to 1
loop: add num, sum    ; add num to sum
      add #1, num     ; add 1 to num
      cmp num, #1000  ; compare num to 1000
      ble loop        ; if num <= 1000, go back to 'loop'
      halt            ; end of program. stop running

Once told to run this program, the computer will perform the repetitive addition task without further human intervention. It will almost never make a mistake and a modern PC can complete the task in about a millionth of a second.^[21]

Bugs

Errors in computer programs are called "bugs". Bugs may be benign and not affect the usefulness of the program, or have only subtle effects. But in some cases they may cause the program to "hang"—become unresponsive to input such as mouse clicks or keystrokes, or to completely fail or "crash". Otherwise benign bugs may sometimes be harnessed for malicious intent by an unscrupulous user writing an "exploit"—code designed to take advantage of a bug and disrupt a computer's proper execution. Bugs are usually not the fault of the computer. Since computers merely execute the instructions they are given, bugs are nearly always the result of programmer error or an oversight made in the program's design.^[22]

Machine code

In most computers, individual instructions are stored as machine code with each instruction being given a unique number (its operation code or opcode for short). The command to add two numbers together would have one opcode, the command to multiply them would have a different opcode and so on. The simplest computers are able to perform any of a handful of different instructions; the more complex computers have several hundred to choose from—each with a unique numerical code. Since the computer's memory is able to store numbers, it can also store the instruction codes. This leads to the important fact that entire programs (which are just lists of these instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer in the same way as numeric data. The fundamental concept of storing programs in the computer's memory alongside the data they operate on is the crux of the von Neumann, or stored program, architecture. In some cases, a computer might store some or all of its program in memory that is kept separate from the data it operates on. This is called the Harvard architecture after the Harvard Mark I computer. Modern von Neumann computers display some traits of the Harvard architecture in their designs, such as in CPU caches.

While it is possible to write computer programs as long lists of numbers (machine language) and while this technique was used with many early computers,^[23] it is extremely tedious and potentially error-prone to do so in practice, especially for complicated programs. Instead, each basic instruction can be given a short name that is indicative of its function and easy to remember—a mnemonic such as ADD, SUB, MULT or JUMP. These mnemonics are collectively known as a computer's assembly language. Converting programs written in assembly language into something the computer can actually understand (machine language) is usually done by a computer program called an assembler. Machine languages and the assembly languages that represent them (collectively termed low-level programming languages) tend to be unique to a particular type of computer. For instance, an ARM architecture computer (such as may be found in a PDA or a hand-held videogame) cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.^[24]

Higher-level languages and program design

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and is also error prone. Therefore, most practical programs are written in more abstract high-level programming languages that are able to express the needs of the programmer more conveniently (and thereby help reduce programmer error). High level languages are usually "compiled" into machine language (or sometimes into assembly language and then into machine language) using another computer program called a compiler.^[25] High level languages are less related to the workings of the target computer than assembly language, and more related to the language and structure of the problem(s) to be solved by the final program. It is therefore often possible to use different compilers to translate the same high level language program into the machine language of many different types of computer. This is part of the means by which software like video games may be made available for different computer architectures such as personal computers and various video game consoles.

The task of developing large software systems presents a significant intellectual challenge. Producing software with an acceptably high reliability within a predictable schedule and budget has historically been difficult; the academic and professional discipline of software engineering concentrates specifically on this challenge.

Function

Main articles: Central processing unit and Microprocessor

A general purpose computer has four main components: the arithmetic logic unit (ALU), the control unit, the memory, and the input and output devices (collectively termed I/O). These parts are interconnected by busses, often made of groups of wires.

Inside each of these parts are thousands to trillions of small electrical circuits which can be turned off or on by means of an electronic switch. Each circuit represents a bit (binary digit) of information so that when the circuit is on it represents a "1", and when off it represents a "0" (in positive logic representation). The circuits are arranged in logic gates so that one or more of the circuits may control the state of one or more of the other circuits.

The control unit, ALU, registers, and basic I/O (and often other hardware closely linked with these) are collectively known as a central processing unit (CPU). Early CPUs were composed of many separate components but since the mid-1970s CPUs have typically been constructed on a single integrated circuit called a microprocessor.

Control unit

Main articles: CPU design and Control unit

Diagram showing how a particular MIPS architecture instruction would be decoded by the control system.

The control unit (often called a control system or central controller) manages the computer's various components; it reads and interprets (decodes) the program instructions, transforming them into a series of control signals which activate other parts of the computer.^[26] Control systems in advanced computers may change the order of some instructions so as to improve performance.

A key component common to all CPUs is the program counter, a special memory cell (a register) that keeps track of which location in memory the next instruction is to be read from.^[27]

The control system's function is as follows—note that this is a simplified description, and some of these steps may be performed concurrently or in a different order depending on the type of CPU:

1. Read the code for the next instruction from the cell indicated by the program counter.


2. Decode the numerical code for the instruction into a set of commands or signals for each of the other systems.


3. Increment the program counter so it points to the next instruction.


4. Read whatever data the instruction requires from cells in memory (or perhaps from an input device). The location of this required data is typically stored within the instruction code.


5. Provide the necessary data to an ALU or register.


6. If the instruction requires an ALU or specialized hardware to complete, instruct the hardware to perform the requested operation.


7. Write the result from the ALU back to a memory location or to a register or perhaps an output device.



8. Jump back to step (1).

Since the program counter is (conceptually) just another set of memory cells, it can be changed by calculations done in the ALU. Adding 100 to the program counter would cause the next instruction to be read from a place 100 locations further down the program. Instructions that modify the program counter are often known as "jumps" and allow for loops (instructions that are repeated by the computer) and often conditional instruction execution (both examples of control flow).

It is noticeable that the sequence of operations that the control unit goes through to process an instruction is in itself like a short computer program—and indeed, in some more complex CPU designs, there is another yet smaller computer called a microsequencer that runs a microcode program that causes all of these events to happen.

Arithmetic/logic unit (ALU)

Main article: Arithmetic logic unit

The ALU is capable of performing two classes of operations: arithmetic and logic.^[28]

The set of arithmetic operations that a particular ALU supports may be limited to adding and subtracting or might include multiplying or dividing, trigonometry functions (sine, cosine, etc.) and square roots. Some can only operate on whole numbers (integers) whilst others use floating point to represent real numbers—albeit with limited precision. However, any computer that is capable of performing just the simplest operations can be programmed to break down the more complex operations into simple steps that it can perform. Therefore, any computer can be programmed to perform any arithmetic operation—although it will take more time to do so if its ALU does not directly support the operation. An ALU may also compare numbers and return boolean truth values (true or false) depending on whether one is equal to, greater than or less than the other ("is 64 greater than 65?").

Logic operations involve Boolean logic: AND, OR, XOR and NOT. These can be useful both for creating complicated conditional statements and processing boolean logic.

Superscalar computers may contain multiple ALUs so that they can process several instructions at the same time.^[29] Graphics processors and computers with SIMD and MIMD features often provide ALUs that can perform arithmetic on vectors and matrices.

Memory

Main article: Computer data storage

Magnetic core memory was the computer memory of choice throughout the 1960s, until it was replaced by semiconductor memory.

A computer's memory can be viewed as a list of cells into which numbers can be placed or read. Each cell has a numbered "address" and can store a single number. The computer can be instructed to "put the number 123 into the cell numbered 1357" or to "add the number that is in cell 1357 to the number that is in cell 2468 and put the answer into cell 1595". The information stored in memory may represent practically anything. Letters, numbers, even computer instructions can be placed into memory with equal ease. Since the CPU does not differentiate between different types of information, it is the software's responsibility to give significance to what the memory sees as nothing but a series of numbers.

In almost all modern computers, each memory cell is set up to store binary numbers in groups of eight bits (called a byte). Each byte is able to represent 256 different numbers (2^8 = 256); either from 0 to 255 or −128 to +127. To store larger numbers, several consecutive bytes may be used (typically, two, four or eight). When negative numbers are required, they are usually stored in two's complement notation. Other arrangements are possible, but are usually not seen outside of specialized applications or historical contexts. A computer can store any kind of information in memory if it can be represented numerically. Modern computers have billions or even trillions of bytes of memory.

The CPU contains a special set of memory cells called registers that can be read and written to much more rapidly than the main memory area. There are typically between two and one hundred registers depending on the type of CPU. Registers are used for the most frequently needed data items to avoid having to access main memory every time data is needed. As data is constantly being worked on, reducing the need to access main memory (which is often slow compared to the ALU and control units) greatly increases the computer's speed.

Computer main memory comes in two principal varieties: random-access memory or RAM and read-only memory or ROM. RAM can be read and written to anytime the CPU commands it, but ROM is pre-loaded with data and software that never changes, so the CPU can only read from it. ROM is typically used to store the computer's initial start-up instructions. In general, the contents of RAM are erased when the power to the computer is turned off, but ROM retains its data indefinitely. In a PC, the ROM contains a specialized program called the BIOS that orchestrates loading the computer's operating system from the hard disk drive into RAM whenever the computer is turned on or reset. In embedded computers, which frequently do not have disk drives, all of the required software may be stored in ROM. Software stored in ROM is often called firmware, because it is notionally more like hardware than software. Flash memory blurs the distinction between ROM and RAM, as it retains its data when turned off but is also rewritable. It is typically much slower than conventional ROM and RAM however, so its use is restricted to applications where high speed is unnecessary.^[30]

In more sophisticated computers there may be one or more RAM cache memories which are slower than registers but faster than main memory. Generally computers with this sort of cache are designed to move frequently needed data into the cache automatically, often without the need for any intervention on the programmer's part.

Input/output (I/O)

Main article: Input/output

Hard disk drives are common storage devices used with computers.

I/O is the means by which a computer exchanges information with the outside world.^[31] Devices that provide input or output to the computer are called peripherals.^[32] On a typical personal computer, peripherals include input devices like the keyboard and mouse, and output devices such as the display and printer. Hard disk drives, floppy disk drives and optical disc drives serve as both input and output devices. Computer networking is another form of I/O.

Often, I/O devices are complex computers in their own right with their own CPU and memory. A graphics processing unit might contain fifty or more tiny computers that perform the calculations necessary to display 3D graphics^{[citation needed]}. Modern desktop computers contain many smaller computers that assist the main CPU in performing I/O.

Multitasking

Main article: Computer multitasking

While a computer may be viewed as running one gigantic program stored in its main memory, in some systems it is necessary to give the appearance of running several programs simultaneously. This is achieved by multitasking i.e. having the computer switch rapidly between running each program in turn.^[33]

One means by which this is done is with a special signal called an interrupt which can periodically cause the computer to stop executing instructions where it was and do something else instead. By remembering where it was executing prior to the interrupt, the computer can return to that task later. If several programs are running "at the same time", then the interrupt generator might be causing several hundred interrupts per second, causing a program switch each time. Since modern computers typically execute instructions several orders of magnitude faster than human perception, it may appear that many programs are running at the same time even though only one is ever executing in any given instant. This method of multitasking is sometimes termed "time-sharing" since each program is allocated a "slice" of time in turn.^[34]

Before the era of cheap computers, the principal use for multitasking was to allow many people to share the same computer.

Seemingly, multitasking would cause a computer that is switching between several programs to run more slowly — in direct proportion to the number of programs it is running. However, most programs spend much of their time waiting for slow input/output devices to complete their tasks. If a program is waiting for the user to click on the mouse or press a key on the keyboard, then it will not take a "time slice" until the event it is waiting for has occurred. This frees up time for other programs to execute so that many programs may be run at the same time without unacceptable speed loss.

Multiprocessing

Main article: Multiprocessing

Cray designed many supercomputers that used multiprocessing heavily.

Some computers are designed to distribute their work across several CPUs in a multiprocessing configuration, a technique once employed only in large and powerful machines such as supercomputers, mainframe computers and servers. Multiprocessor and multi-core (multiple CPUs on a single integrated circuit) personal and laptop computers are now widely available, and are being increasingly used in lower-end markets as a result.

Supercomputers in particular often have highly unique architectures that differ significantly from the basic stored-program architecture and from general purpose computers.^[35] They often feature thousands of CPUs, customized high-speed interconnects, and specialized computing hardware. Such designs tend to be useful only for specialized tasks due to the large scale of program organization required to successfully utilize most of the available resources at once. Supercomputers usually see usage in large-scale simulation, graphics rendering, and cryptography applications, as well as with other so-called "embarrassingly parallel" tasks.

Networking and the Internet

Main articles: Computer networking and Internet

Visualization of a portion of the routes on the Internet.

Computers have been used to coordinate information between multiple locations since the 1950s. The U.S. military's SAGE system was the first large-scale example of such a system, which led to a number of special-purpose commercial systems like Sabre.^[36]

In the 1970s, computer engineers at research institutions throughout the United States began to link their computers together using telecommunications technology. This effort was funded by ARPA (now DARPA), and the computer network that it produced was called the ARPANET.^[37] The technologies that made the Arpanet possible spread and evolved.

In time, the network spread beyond academic and military institutions and became known as the Internet. The emergence of networking involved a redefinition of the nature and boundaries of the computer. Computer operating systems and applications were modified to include the ability to define and access the resources of other computers on the network, such as peripheral devices, stored information, and the like, as extensions of the resources of an individual computer. Initially these facilities were available primarily to people working in high-tech environments, but in the 1990s the spread of applications like e-mail and the World Wide Web, combined with the development of cheap, fast networking technologies like Ethernet and ADSL saw computer networking become almost ubiquitous. In fact, the number of computers that are networked is growing phenomenally. A very large proportion of personal computers regularly connect to the Internet to communicate and receive information. "Wireless" networking, often utilizing mobile phone networks, has meant networking is becoming increasingly ubiquitous even in mobile computing environments.

Misconceptions

A computer does not need to be electric, nor even have a processor, nor RAM, nor even hard disk. The minimal definition of a computer is anything that transforms information in a purposeful way.

Required technology

Main article: Unconventional computing

Computational systems as flexible as a personal computer can be built out of almost anything. For example, a computer can be made out of billiard balls (billiard ball computer); this is an unintuitive and pedagogical example that a computer can be made out of almost anything. More realistically, modern computers are made out of transistors made of photolithographed semiconductors.

Historically, computers evolved from mechanical computers and eventually from vacuum tubes to transistors.

There is active research to make computers out of many promising new types of technology, such as optical computing, DNA computers, neural computers, and quantum computers. Some of these can easily tackle problems that modern computers cannot (such as how quantum computers can break some modern encryption algorithms by quantum factoring).

Computer architecture paradigms

Some different paradigms of how to build a computer from the ground-up:

RAM machines

These are the types of computers with a CPU, computer memory, etc., which understand basic instructions in a machine language. The concept evolved from the Turing machine.

Brains

Brains are massively parallel processors made of neurons, wired in intricate patterns, that communicate via electricity and neurotransmitter chemicals.

Programming languages

Such as the lambda calculus, or modern programming languages, are virtual computers built on top of other computers.

Cellular automata

For example, the game of Life can create "gliders" and "loops" and other constructs that transmit information; this paradigm can be applied to DNA computing, chemical computing, etc.

Groups and committees

The linking of multiple computers (brains) is itself a computer

Logic gates are a common abstraction which can apply to most of the above digital or analog paradigms.

The ability to store and execute lists of instructions called programs makes computers extremely versatile, distinguishing them from calculators. The Church–Turing thesis is a mathematical statement of this versatility: any computer with a minimum capability (being Turing-complete) is, in principle, capable of performing the same tasks that any other computer can perform. Therefore any type of computer (netbook, supercomputer, cellular automaton, etc.) is able to perform the same computational tasks, given enough time and storage capacity.

Limited-function computers

Conversely, a computer which is limited in function (one that is not "Turing-complete") cannot simulate arbitrary things. For example, simple four-function calculators cannot simulate a real computer without human intervention. As a more complicated example, without the ability to program a gaming console, it can never accomplish what a programmable calculator from the 1990s could (given enough time); the system as a whole is not Turing-complete, even though it contains a Turing-complete component (the microprocessor). Living organisms (the body, not the brain) are also limited-function computers designed to make copies of themselves; they cannot be reprogrammed without genetic engineering.

Virtual computers

A "computer" is commonly considered to be a physical device. However, one can create a computer program which describes how to run a different computer, i.e. "simulating a computer in a computer". Not only is this a constructive proof of the Church-Turing thesis, but is also extremely common in all modern computers. For example, some programming languages use something called an interpreter, which is a simulated computer built on top of the basic computer; this allows programmers to write code (computer input) in a different language than the one understood by the base computer (the alternative is to use a compiler). Additionally, virtual machines are simulated computers which virtually replicate a physical computer in software, and are very commonly used by IT. Virtual machines are also a common technique used to create emulators, such game console emulators.

Further topics

• Glossary of computers

Artificial intelligence

A computer will solve problems in exactly the way they are programmed to, without regard to efficiency nor alternative solutions nor possible shortcuts nor possible errors in the code. Computer programs which learn and adapt are part of the emerging field of artificial intelligence and machine learning.

Hardware

The term hardware covers all of those parts of a computer that are tangible objects. Circuits, displays, power supplies, cables, keyboards, printers and mice are all hardware.

History of computing hardware

First Generation (Mechanical/Electromechanical)	Calculators	Antikythera mechanism, Difference engine, Norden bombsight
	Programmable Devices	Jacquard loom, Analytical engine, Harvard Mark I, Z3
Second Generation (Vacuum Tubes)	Calculators	Atanasoff–Berry Computer, IBM 604, UNIVAC 60, UNIVAC 120
	Programmable Devices	Colossus, ENIAC, Manchester Small-Scale Experimental Machine, EDSAC, Manchester Mark 1, Ferranti Pegasus, Ferranti Mercury, CSIRAC, EDVAC, UNIVAC I, IBM 701, IBM 702, IBM 650, Z22
Third Generation (Discrete transistors and SSI, MSI, LSI Integrated circuits)	Mainframes	IBM 7090, IBM 7080, IBM System/360, BUNCH
	Minicomputer	PDP-8, PDP-11, IBM System/32, IBM System/36
Fourth Generation (VLSI integrated circuits)	Minicomputer	VAX, IBM System i
	4-bit microcomputer	Intel 4004, Intel 4040
	8-bit microcomputer	Intel 8008, Intel 8080, Motorola 6800, Motorola 6809, MOS Technology 6502, Zilog Z80
	16-bit microcomputer	Intel 8088, Zilog Z8000, WDC 65816/65802
	32-bit microcomputer	Intel 80386, Pentium, Motorola 68000, ARM architecture
	64-bit microcomputer[38]	Alpha, MIPS, PA-RISC, PowerPC, SPARC, x86-64
	Embedded computer	Intel 8048, Intel 8051
	Personal computer	Desktop computer, Home computer, Laptop computer, Personal digital assistant (PDA), Portable computer, Tablet PC, Wearable computer
Theoretical/experimental	Quantum computer, Chemical computer, DNA computing, Optical computer, Spintronics based computer

Other Hardware Topics

Peripheral device (Input/output)	Input	Mouse, Keyboard, Joystick, Image scanner, Webcam, Graphics tablet, Microphone
	Output	Monitor, Printer, Loudspeaker
	Both	Floppy disk drive, Hard disk drive, Optical disc drive, Teleprinter
Computer busses	Short range	RS-232, SCSI, PCI, USB
	Long range (Computer networking)	Ethernet, ATM, FDDI

Software

Main article: Computer software

Software refers to parts of the computer which do not have a material form, such as programs, data, protocols, etc. When software is stored in hardware that cannot easily be modified (such as BIOS ROM in an IBM PC compatible), it is sometimes called "firmware" to indicate that it falls into an uncertain area somewhere between hardware and software.

Computer software

Operating system	Unix and BSD	UNIX System V, IBM AIX, HP-UX, Solaris (SunOS), IRIX, List of BSD operating systems
	GNU/Linux	List of Linux distributions, Comparison of Linux distributions
	Microsoft Windows	Windows 95, Windows 98, Windows NT, Windows 2000, Windows XP, Windows Vista, Windows 7
	DOS	86-DOS (QDOS), PC-DOS, MS-DOS, DR-DOS, FreeDOS
	Mac OS	Mac OS classic, Mac OS X
	Embedded and real-time	List of embedded operating systems
	Experimental	Amoeba, Oberon/Bluebottle, Plan 9 from Bell Labs
Library	Multimedia	DirectX, OpenGL, OpenAL
	Programming library	C standard library, Standard Template Library
Data	Protocol	TCP/IP, Kermit, FTP, HTTP, SMTP
	File format	HTML, XML, JPEG, MPEG, PNG
User interface	Graphical user interface (WIMP)	Microsoft Windows, GNOME, KDE, QNX Photon, CDE, GEM, Aqua
	Text-based user interface	Command-line interface, Text user interface
Application	Office suite	Word processing, Desktop publishing, Presentation program, Database management system, Scheduling & Time management, Spreadsheet, Accounting software
	Internet Access	Browser, E-mail client, Web server, Mail transfer agent, Instant messaging
	Design and manufacturing	Computer-aided design, Computer-aided manufacturing, Plant management, Robotic manufacturing, Supply chain management
	Graphics	Raster graphics editor, Vector graphics editor, 3D modeler, Animation editor, 3D computer graphics, Video editing, Image processing
	Audio	Digital audio editor, Audio playback, Mixing, Audio synthesis, Computer music
	Software engineering	Compiler, Assembler, Interpreter, Debugger, Text editor, Integrated development environment, Software performance analysis, Revision control, Software configuration management
	Educational	Edutainment, Educational game, Serious game, Flight simulator
	Games	Strategy, Arcade, Puzzle, Simulation, First-person shooter, Platform, Massively multiplayer, Interactive fiction
	Misc	Artificial intelligence, Antivirus software, Malware scanner, Installer/Package management systems, File manager

Programming languages

Main article: Programming language

Programming languages provide various ways of specifying programs for computers to run. Unlike natural languages, programming languages are designed to permit no ambiguity and to be concise. They are purely written languages and are often difficult to read aloud. They are generally either translated into machine code by a compiler or an assembler before being run, or translated directly at run time by an interpreter. Sometimes programs are executed by a hybrid method of the two techniques. There are thousands of different programming languages—some intended to be general purpose, others useful only for highly specialized applications.

Programming languages

Lists of programming languages	Timeline of programming languages, List of programming languages by category, Generational list of programming languages, List of programming languages, Non-English-based programming languages
Commonly used Assembly languages	ARM, MIPS, x86
Commonly used high-level programming languages	Ada, BASIC, C, C++, C#, COBOL, Fortran, Java, Lisp, Pascal, Object Pascal
Commonly used Scripting languages	Bourne script, JavaScript, Python, Ruby, PHP, Perl

Professions and organizations

As the use of computers has spread throughout society, there are an increasing number of careers involving computers.

Computer-related professions

Hardware-related	Electrical engineering, Electronic engineering, Computer engineering, Telecommunications engineering, Optical engineering, Nanoengineering
Software-related	Computer science, Desktop publishing, Human–computer interaction, Information technology, Information systems, Computational science, Software engineering, Video game industry, Web design

The need for computers to work well together and to be able to exchange information has spawned the need for many standards organizations, clubs and societies of both a formal and informal nature.

Organizations

Standards groups	ANSI, IEC, IEEE, IETF, ISO, W3C
Professional Societies	ACM, AIS, IET, IFIP, BCS
Free/Open source software groups	Free Software Foundation, Mozilla Foundation, Apache Software Foundation

See also

Information technology portal

• Computability theory


• Computer security


• Computer insecurity


• List of computer term etymologies


• List of fictional computers


• Pulse computation

Notes

1. ^ In 1946, ENIAC required an estimated 174 kW. By comparison, a modern laptop computer may use around 30 W; nearly six thousand times less. "Approximate Desktop & Notebook Power Usage". University of Pennsylvania. http://www.upenn.edu/computing/provider/docs/hardware/powerusage.html. Retrieved 2009-06-20. 



2. ^ Early computers such as Colossus and ENIAC were able to process between 5 and 100 operations per second. A modern "commodity" microprocessor (as of 2007) can process billions of operations per second, and many of these operations are more complicated and useful than early computer operations. "Intel Core2 Duo Mobile Processor: Features". Intel Corporation. http://www.intel.com/cd/channel/reseller/asmo-na/eng/products/mobile/processors/core2duo_m/feature/index.htm. Retrieved 2009-06-20. 



3. ^ computer, n.. Oxford English Dictionary (2 ed.). Oxford University Press. 1989. http://dictionary.oed.com/. Retrieved 2009-04-10 


4. ^ "Discovering How Greeks Computed in 100 B.C.". The New York Times. 31 July 2008. http://www.nytimes.com/2008/07/31/science/31computer.html?hp. Retrieved 27 March 2010. 



5. ^ "Heron of Alexandria". http://www.mlahanas.de/Greeks/HeronAlexandria2.htm. Retrieved 2008-01-15. 


6. ^ ^{a b} Ancient Discoveries, Episode 11: Ancient Robots. History Channel. http://www.youtube.com/watch?v=rxjbaQl0ad8. Retrieved 2008-09-06 



7. ^ Howard R. Turner (1997), Science in Medieval Islam: An Illustrated Introduction, p. 184, University of Texas Press, ISBN 0-292-78149-0


8. ^ Donald Routledge Hill, "Mechanical Engineering in the Medieval Near East", Scientific American, May 1991, pp. 64–9 (cf. Donald Routledge Hill, Mechanical Engineering)



9. ^ From cave paintings to the internet HistoryofScience.com


10. ^ See: Anthony Hyman, ed., Science and Reform: Selected Works of Charles Babbage (Cambridge, England: Cambridge University Press, 1989), page 298. It is in the collection of the Science Museum in London, England. (Delve (2007), page 99.)


11. ^ The analytical engine should not be confused with Babbage's difference engine which was a non-programmable mechanical calculator.



12. ^ "Columbia University Computing History: Herman Hollerith". Columbia.edu. http://www.columbia.edu/acis/history/hollerith.html. Retrieved 2010-12-11. 


13. ^ ^{a b} "Alan Turing – Time 100 People of the Century". Time Magazine. http://205.188.238.181/time/time100/scientist/profile/turing.html. Retrieved 2009-06-13. "The fact remains that everyone who taps at a keyboard, opening a spreadsheet or a word-processing program, is working on an incarnation of a Turing machine" 



14. ^ "Atanasoff-Berry Computer". http://energysciencenews.com/phpBB3/viewtopic.php?f=1&t=98&p=264#p264. Retrieved 2010-11-20. 


15. ^ "Spiegel: The inventor of the computer's biography was published". Spiegel.de. 2009-09-28. http://www.spiegel.de/netzwelt/gadgets/0,1518,651776,00.html. Retrieved 2010-12-11. 



16. ^ "Inventor Profile: George R. Stibitz". National Inventors Hall of Fame Foundation, Inc.. http://www.invent.org/hall_of_fame/140.html. 


17. ^ Rojas, R. (1998). "How to make Zuse's Z3 a universal computer". IEEE Annals of the History of Computing 20 (3): 51–54. doi:10.1109/85.707574. 



18. ^ B. Jack Copeland, ed., Colossus: The Secrets of Bletchley Park's Codebreaking Computers, Oxford University Press, 2006


19. ^ ""Robot Mathematician Knows All The Answers", October 1944, Popular Science". Books.google.com. http://books.google.com/books?id=PyEDAAAAMBAJ&pg=PA86&dq=motor+gun+boat&hl=en&ei=LxTqTMfGI4-bnwfEyNiWDQ&sa=X&oi=book_result&ct=result&resnum=6&ved=0CEIQ6AEwBQ#v=onepage&q=motor%20gun%20boat&f=true. Retrieved 2010-12-11. 



20. ^ Lavington 1998, p. 37


21. ^ This program was written similarly to those for the PDP-11 minicomputer and shows some typical things a computer can do. All the text after the semicolons are comments for the benefit of human readers. These have no significance to the computer and are ignored. (Digital Equipment Corporation 1972)



22. ^ It is not universally true that bugs are solely due to programmer oversight. Computer hardware may fail or may itself have a fundamental problem that produces unexpected results in certain situations. For instance, the Pentium FDIV bug caused some Intel microprocessors in the early 1990s to produce inaccurate results for certain floating point division operations. This was caused by a flaw in the microprocessor design and resulted in a partial recall of the affected devices.


23. ^ Even some later computers were commonly programmed directly in machine code. Some minicomputers like the DEC PDP-8 could be programmed directly from a panel of switches. However, this method was usually used only as part of the booting process. Most modern computers boot entirely automatically by reading a boot program from some non-volatile memory.



24. ^ However, there is sometimes some form of machine language compatibility between different computers. An x86-64 compatible microprocessor like the AMD Athlon 64 is able to run most of the same programs that an Intel Core 2 microprocessor can, as well as programs designed for earlier microprocessors like the Intel Pentiums and Intel 80486. This contrasts with very early commercial computers, which were often one-of-a-kind and totally incompatible with other computers.



25. ^ High level languages are also often interpreted rather than compiled. Interpreted languages are translated into machine code on the fly, while running, by another program called an interpreter.


26. ^ The control unit's role in interpreting instructions has varied somewhat in the past. Although the control unit is solely responsible for instruction interpretation in most modern computers, this is not always the case. Many computers include some instructions that may only be partially interpreted by the control system and partially interpreted by another device. This is especially the case with specialized computing hardware that may be partially self-contained. For example, EDVAC, one of the earliest stored-program computers, used a central control unit that only interpreted four instructions. All of the arithmetic-related instructions were passed on to its arithmetic unit and further decoded there.


27. ^ Instructions often occupy more than one memory address, so the program counters usually increases by the number of memory locations required to store one instruction.



28. ^ David J. Eck (2000). The Most Complex Machine: A Survey of Computers and Computing. A K Peters, Ltd.. p. 54. ISBN 9781568811284. 


29. ^ Erricos John Kontoghiorghes (2006). Handbook of Parallel Computing and Statistics. CRC Press. p. 45. ISBN 9780824740672. 



30. ^ Flash memory also may only be rewritten a limited number of times before wearing out, making it less useful for heavy random access usage. (Verma & Mielke 1988)


31. ^ Donald Eadie (1968). Introduction to the Basic Computer. Prentice-Hall. p. 12. 


32. ^ Arpad Barna; Dan I. Porat (1976). Introduction to Microcomputers and the Microprocessors. Wiley. p. 85. ISBN 9780471050513. 



33. ^ Jerry Peek; Grace Todino, John Strang (2002). Learning the UNIX Operating System: A Concise Guide for the New User. O'Reilly. p. 130. ISBN 9780596002619. 


34. ^ Gillian M. Davis (2002). Noise Reduction in Speech Applications. CRC Press. p. 111. ISBN 9780849309496. 



35. ^ However, it is also very common to construct supercomputers out of many pieces of cheap commodity hardware; usually individual computers connected by networks. These so-called computer clusters can often provide supercomputer performance at a much lower cost than customized designs. While custom architectures are still used for most of the most powerful supercomputers, there has been a proliferation of cluster computers in recent years. (TOP500 2006)


36. ^ Agatha C. Hughes (2000). Systems, Experts, and Computers. MIT Press. p. 161. ISBN 9780262082853. "The experience of SAGE helped make possible the first truly large-scale commercial real-time network: the SABRE computerized airline reservations system..." 



37. ^ "A Brief History of the Internet". Internet Society. http://www.isoc.org/internet/history/brief.shtml. Retrieved 2008-09-20. 


38. ^ Most major 64-bit instruction set architectures are extensions of earlier designs. All of the architectures listed in this table, except for Alpha, existed in 32-bit forms before their 64-bit incarnations were introduced.

References

• ^a Kempf, Karl (1961). Historical Monograph: Electronic Computers Within the Ordnance Corps. Aberdeen Proving Ground (United States Army). http://ed-thelen.org/comp-hist/U-S-Ord-61.html. 



• ^a Phillips, Tony (2000). "The Antikythera Mechanism I". American Mathematical Society. http://www.math.sunysb.edu/~tony/whatsnew/column/antikytheraI-0400/kyth1.html. Retrieved 2006-04-05. 


• ^a Shannon, Claude Elwood (1940). A symbolic analysis of relay and switching circuits. Massachusetts Institute of Technology. http://hdl.handle.net/1721.1/11173. 



• Digital Equipment Corporation (1972) (PDF). PDP-11/40 Processor Handbook. Maynard, MA: Digital Equipment Corporation. http://bitsavers.vt100.net/dec/www.computer.museum.uq.edu.au_mirror/D-09-30_PDP11-40_Processor_Handbook.pdf. 


• Verma, G.; Mielke, N. (1988). Reliability performance of ETOX based flash memories. IEEE International Reliability Physics Symposium. 


• Meuer, Hans; Strohmaier, Erich; Simon, Horst; Dongarra, Jack (2006-11-13). "Architectures Share Over Time". TOP500. http://www.top500.org/lists/2006/11/overtime/Architectures. Retrieved 2006-11-27. 



• Lavington, Simon (1998). A History of Manchester Computers (2 ed.). Swindon: The British Computer Society. ISBN 0902505018 


• Stokes, Jon (2007). Inside the Machine: An Illustrated Introduction to Microprocessors and Computer Architecture. San Francisco: No Starch Press. ISBN 978-1-59327-104-6. 

External links

Find more about Computer on Wikipedia's sister projects:
	Definitions from Wiktionary
	Images and media from Commons
	Learning resources from Wikiversity
	News stories from Wikinews
	Quotations from Wikiquote
	Source texts from Wikisource
	Textbooks from Wikibooks

• A Brief History of Computing - slideshow by Life magazine

Retrieved from "http://en.wikipedia.org/wiki/Computer"

Categories: Computers | Computing

Hidden categories: Wikipedia indefinitely semi-protected pages | Wikipedia indefinitely move-protected pages | All pages needing factual verification | Wikipedia articles needing factual verification from September 2010 | All articles with unsourced statements | Articles with unsourced statements from February 2010 | Articles with unsourced statements from December 2007 | Use dmy dates from September 2010