Saturday, 13 March 2010

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A bank is a financial institution that accepts deposits and channels those deposits into lending activities. Banks primarily provide financial services to customers while enriching investors. Government restrictions on financial activities by banks vary over time and location. Banks are important players in financial markets and offer services such as investment funds and loans. In some countries such as Germany, banks have historically owned major stakes in industrial corporations while in other countries such as the United States banks are prohibited from owning non-financial companies. In Japan, banks are usually the nexus of a cross-share holding entity known as the keiretsu. In France, bancassurance is prevalent, as most banks offer insurance services (and now real estate services) to their clients.

The level of government regulation of the banking industry varies widely, with countries such as Iceland, having relatively light regulation of the banking sector, and countries such as China having a wide variety of regulations but no systematic process that can be followed typical of a communist system.

The oldest bank still in existence is Monte dei Paschi di Siena, headquartered in Siena, Italy, which has been operating continuously since 1472.[1]

* 16 References

* 17 Further reading

[edit] History

Main article: History of banking

The very first state deposit bank, Banco di San Giorgio (Bank of St. George), was founded in 1407 at Genoa, Italy.[2]

[edit] Origin of the word

Silver drachm coin from Trapezus, 4th century BC

The name bank derives from the Italian word banco "desk/bench", used during the Renaissance by Jewish Florentine bankers, who used to make their transactions above a desk covered by a green tablecloth.[3] However, there are traces of banking activity even in ancient times, which indicates that the word 'bank' might not necessarily come from the word 'banco'.

In fact, the word traces its origins back to the Ancient Roman Empire, where moneylenders would set up their stalls in the middle of enclosed courtyards called macella on a long bench called a bancu, from which the words banco and bank are derived. As a moneychanger, the merchant at the bancu did not so much invest money as merely convert the foreign currency into the only legal tender in Rome—that of the Imperial Mint.[4]

The earliest evidence of money-changing activity is depicted on a silver drachm coin from ancient Hellenic colony Trapezus on the Black Sea, modern Trabzon, c. 350–325 BC, presented in the British Museum in London. The coin shows a banker's table (trapeza) laden with coins, a pun on the name of the city.

In fact, even today in Modern Greek the word Trapeza (Τράπεζα) means both a table and a bank.

[edit] Traditional banking activities

Large door to an old bank vault.

Banks act as payment agents by conducting checking or current accounts for customers, paying cheques drawn by customers on the bank, and collecting cheques deposited to customers' current accounts. Banks also enable customer payments via other payment methods such as telegraphic transfer, EFTPOS, and ATM.

Banks borrow money by accepting funds deposited on current accounts, by accepting term deposits, and by issuing debt securities such as banknotes and bonds. Banks lend money by making advances to customers on current accounts, by making installment loans, and by investing in marketable debt securities and other forms of money lending.

Banks provide almost all payment services, and a bank account is considered indispensable by most businesses, individuals and governments. Non-banks that provide payment services such as remittance companies are not normally considered an adequate substitute for having a bank account.

Banks borrow most funds from households and non-financial businesses, and lend most funds to households and non-financial businesses, but non-bank lenders provide a significant and in many cases adequate substitute for bank loans, and money market funds, cash management trusts and other non-bank financial institutions in many cases provide an adequate substitute to banks for lending savings to.[clarification needed]

[edit] Entry regulation

Main article: Banking regulation

Currently in most jurisdictions commercial banks are regulated by government entities and require a special bank licence to operate.

Usually the definition of the business of banking for the purposes of regulation is extended to include acceptance of deposits, even if they are not repayable to the customer's order—although money lending, by itself, is generally not included in the definition.

Unlike most other regulated industries, the regulator is typically also a participant in the market, i.e. a government-owned (central) bank. Central banks also typically have a monopoly on the business of issuing banknotes. However, in some countries this is not the case. In the UK, for example, the Financial Services Authority licences banks, and some commercial banks (such as the Bank of Scotland) issue their own banknotes in addition to those issued by the Bank of England, the UK government's central bank.

[edit] Definition

Cathay Bank in Boston's Chinatown

The definition of a bank varies from country to country.

Under English common law, a banker is defined as a person who carries on the business of banking, which is specified as:[5]

* conducting current accounts for his customers

* paying cheques drawn on him, and

* collecting cheques for his customers.

In most English common law jurisdictions there is a Bills of Exchange Act that codifies the law in relation to negotiable instruments, including cheques, and this Act contains a statutory definition of the term banker: banker includes a body of persons, whether incorporated or not, who carry on the business of banking' (Section 2, Interpretation). Although this definition seems circular, it is actually functional, because it ensures that the legal basis for bank transactions such as cheques does not depend on how the bank is organised or regulated.

The business of banking is in many English common law countries not defined by statute but by common law, the definition above. In other English common law jurisdictions there are statutory definitions of the business of banking or banking business. When looking at these definitions it is important to keep in mind that they are defining the business of banking for the purposes of the legislation, and not necessarily in general. In particular, most of the definitions are from legislation that has the purposes of entry regulating and supervising banks rather than regulating the actual business of banking. However, in many cases the statutory definition closely mirrors the common law one. Examples of statutory definitions:

* "banking business" means the business of receiving money on current or deposit account, paying and collecting cheques drawn by or paid in by customers, the making of advances to customers, and includes such other business as the Authority may prescribe for the purposes of this Act; (Banking Act (Singapore), Section 2, Interpretation).

* "banking business" means the business of either or both of the following:

1. receiving from the general public money on current, deposit, savings or other similar account repayable on demand or within less than [3 months] ... or with a period of call or notice of less than that period;

2. paying or collecting cheques drawn by or paid in by customers[6]

Since the advent of EFTPOS (Electronic Funds Transfer at Point Of Sale), direct credit, direct debit and internet banking, the cheque has lost its primacy in most banking systems as a payment instrument. This has led legal theorists to suggest that the cheque based definition should be broadened to include financial institutions that conduct current accounts for customers and enable customers to pay and be paid by third parties, even if they do not pay and collect cheques.[7]

[edit] Accounting for bank accounts

Suburban branch bank

Bank statements are accounting records produced by banks under the various accounting standards of the world. Under GAAP and IFRS there are two kinds of accounts: debit and credit. Credit accounts are Revenue, Equity and Liabilities. Debit Accounts are Assets and Expenses. This means you credit a credit account to increase its balance, and you debit a debit account to decrease its balance.[8]

This also means you debit your savings account every time you deposit money into it (and the account is normally in deficit), while you credit your credit card account every time you spend money from it (and the account is normally in credit).

However, if you read your bank statement, it will say the opposite—that you credit your account when you deposit money, and you debit it when you withdraw funds. If you have cash in your account, you have a positive (or credit) balance; if you are overdrawn, you have a negative (or deficit) balance.

The reason for this is that the bank, and not you, has produced the bank statement. Your savings might be your assets, but the bank's liability, so they are credit accounts (which should have a positive balance). Conversely, your loans are your liabilities but the bank's assets, so they are debit accounts (which should also have a positive balance).

Where bank transactions, balances, credits and debits are discussed below, they are done so from the viewpoint of the account holder—which is traditionally what most people are used to seeing.

[edit] Wider commercial role

The commercial role of banks is not limited to banking, and includes:

* issue of banknotes (promissory notes issued by a banker and payable to bearer on demand)

* processing of payments by way of telegraphic transfer, EFTPOS, internet banking or other means

* issuing bank drafts and bank cheques

* accepting money on term deposit

* lending money by way of overdraft, installment loan or otherwise

* providing documentary and standby letters of credit (trade finance), guarantees, performance bonds, securities underwriting commitments and other forms of off-balance sheet exposures

* safekeeping of documents and other items in safe deposit boxes

* currency exchange

* acting as a 'financial supermarket' for the sale, distribution or brokerage, with or without advice, of insurance, unit trusts and similar financial products

[edit] Economic functions

The economic functions of banks include:

1. issue of money, in the form of banknotes and current accounts subject to cheque or payment at the customer's order. These claims on banks can act as money because they are negotiable and/or repayable on demand, and hence valued at par. They are effectively transferable by mere delivery, in the case of banknotes, or by drawing a cheque that the payee may bank or cash.

2. netting and settlement of payments – banks act as both collection and paying agents for customers, participating in interbank clearing and settlement systems to collect, present, be presented with, and pay payment instruments. This enables banks to economise on reserves held for settlement of payments, since inward and outward payments offset each other. It also enables the offsetting of payment flows between geographical areas, reducing the cost of settlement between them.

3. credit intermediation – banks borrow and lend back-to-back on their own account as middle men.

4. credit quality improvement – banks lend money to ordinary commercial and personal borrowers (ordinary credit quality), but are high quality borrowers. The improvement comes from diversification of the bank's assets and capital which provides a buffer to absorb losses without defaulting on its obligations. However, banknotes and deposits are generally unsecured; if the bank gets into difficulty and pledges assets as security, to raise the funding it needs to continue to operate, this puts the note holders and depositors in an economically subordinated position.

5. maturity transformation – banks borrow more on demand debt and short term debt, but provide more long term loans. In other words, they borrow short and lend long. With a stronger credit quality than most other borrowers, banks can do this by aggregating issues (e.g. accepting deposits and issuing banknotes) and redemptions (e.g. withdrawals and redemptions of banknotes), maintaining reserves of cash, investing in marketable securities that can be readily converted to cash if needed, and raising replacement funding as needed from various sources (e.g. wholesale cash markets and securities markets).

[edit] Law of banking

Banking law is based on a contractual analysis of the relationship between the bank (defined above) and the customer—defined as any entity for which the bank agrees to conduct an account.

The law implies rights and obligations into this relationship as follows:

1. The bank account balance is the financial position between the bank and the customer: when the account is in credit, the bank owes the balance to the customer; when the account is overdrawn, the customer owes the balance to the bank.

2. The bank agrees to pay the customer's cheques up to the amount standing to the credit of the customer's account, plus any agreed overdraft limit.

3. The bank may not pay from the customer's account without a mandate from the customer, e.g. a cheque drawn by the customer.

4. The bank agrees to promptly collect the cheques deposited to the customer's account as the customer's agent, and to credit the proceeds to the customer's account.

5. The bank has a right to combine the customer's accounts, since each account is just an aspect of the same credit relationship.

6. The bank has a lien on cheques deposited to the customer's account, to the extent that the customer is indebted to the bank.

7. The bank must not disclose details of transactions through the customer's account—unless the customer consents, there is a public duty to disclose, the bank's interests require it, or the law demands it.

8. The bank must not close a customer's account without reasonable notice, since cheques are outstanding in the ordinary course of business for several days.

These implied contractual terms may be modified by express agreement between the customer and the bank. The statutes and regulations in force within a particular jurisdiction may also modify the above terms and/or create new rights, obligations or limitations relevant to the bank-customer relationship.

Some types of financial institution, such as building societies and credit unions, may be partly or wholly exempt from bank licence requirements, and therefore regulated under separate rules.

The requirements for the issue of a bank licence vary between jurisdictions but typically include:

1. Minimum capital

2. Minimum capital ratio

3. 'Fit and Proper' requirements for the bank's controllers, owners, directors, and/or senior officers

4. Approval of the bank's business plan as being sufficiently prudent and plausible.

[edit] Banking channels

Banks offer many different channels to access their banking and other services:

* A branch, banking centre or financial centre is a retail location where a bank or financial institution offers a wide array of face-to-face service to its customers.

* ATM is a computerised telecommunications device that provides a financial institution's customers a method of financial transactions in a public space without the need for a human clerk or bank teller. Most banks now have more ATMs than branches, and ATMs are providing a wider range of services to a wider range of users. For example in Hong Kong, most ATMs enable anyone to deposit cash to any customer of the bank's account by feeding in the notes and entering the account number to be credited. Also, most ATMs enable card holders from other banks to get their account balance and withdraw cash, even if the card is issued by a foreign bank.

* Mail is part of the postal system which itself is a system wherein written documents typically enclosed in envelopes, and also small packages containing other matter, are delivered to destinations around the world. This can be used to deposit cheques and to send orders to the bank to pay money to third parties. Banks also normally use mail to deliver periodic account statements to customers.

* Telephone banking is a service provided by a financial institution which allows its customers to perform transactions over the telephone. This normally includes bill payments for bills from major billers (e.g. for electricity).

* Online banking is a term used for performing transactions, payments etc. over the Internet through a bank, credit union or building society's secure website.

* Mobile banking is a method of using one's mobile phone to conduct simple banking transactions by remotely linking into a banking network.

* Video banking is a term used for performing banking transactions or professional banking consultations via a remote video and audio connection. Video banking can be performed via purpose built banking transaction machines (similar to an Automated teller machine), or via a videoconference enabled bank branch.

[edit] Types of banks

Banks' activities can be divided into retail banking, dealing directly with individuals and small businesses; business banking, providing services to mid-market business; corporate banking, directed at large business entities; private banking, providing wealth management services to high net worth individuals and families; and investment banking, relating to activities on the financial markets. Most banks are profit-making, private enterprises. However, some are owned by government, or are non-profit organizations.

Central banks are normally government-owned and charged with quasi-regulatory responsibilities, such as supervising commercial banks, or controlling the cash interest rate. They generally provide liquidity to the banking system and act as the lender of last resort in event of a crisis.

[edit] Types of retail banks

National Bank of the Republic, Salt Lake City 1908

ATM AL RAJHI BANK

National Copper Bank, Salt Lake City 1911

* Commercial bank: the term used for a normal bank to distinguish it from an investment bank. After the Great Depression, the U.S. Congress required that banks only engage in banking activities, whereas investment banks were limited to capital market activities. Since the two no longer have to be under separate ownership, some use the term "commercial bank" to refer to a bank or a division of a bank that mostly deals with deposits and loans from corporations or large businesses.

* Community Banks: locally operated financial institutions that empower employees to make local decisions to serve their customers and the partners.

* Community development banks: regulated banks that provide financial services and credit to under-served markets or populations.

* Postal savings banks: savings banks associated with national postal systems.

* Private banks: banks that manage the assets of high net worth individuals.

* Offshore banks: banks located in jurisdictions with low taxation and regulation. Many offshore banks are essentially private banks.

* Savings bank: in Europe, savings banks take their roots in the 19th or sometimes even 18th century. Their original objective was to provide easily accessible savings products to all strata of the population. In some countries, savings banks were created on public initiative; in others, socially committed individuals created foundations to put in place the necessary infrastructure. Nowadays, European savings banks have kept their focus on retail banking: payments, savings products, credits and insurances for individuals or small and medium-sized enterprises. Apart from this retail focus, they also differ from commercial banks by their broadly decentralised distribution network, providing local and regional outreach—and by their socially responsible approach to business and society.

* Building societies and Landesbanks: institutions that conduct retail banking.

* Ethical banks: banks that prioritize the transparency of all operations and make only what they consider to be socially-responsible investments.

* Islamic banks: Banks that transact according to Islamic principles.

[edit] Types of investment banks

* Investment banks "underwrite" (guarantee the sale of) stock and bond issues, trade for their own accounts, make markets, and advise corporations on capital market activities such as mergers and acquisitions.

* Merchant banks were traditionally banks which engaged in trade finance. The modern definition, however, refers to banks which provide capital to firms in the form of shares rather than loans. Unlike venture capital firms, they tend not to invest in new companies.

[edit] Both combined

* Universal banks, more commonly known as financial services companies, engage in several of these activities. These big banks are very diversified groups that, among other services, also distribute insurance— hence the term bancassurance, a portmanteau word combining "banque or bank" and "assurance", signifying that both banking and insurance are provided by the same corporate entity.

[edit] Other types of banks

* Islamic banks adhere to the concepts of Islamic law. This form of banking revolves around several well-established principles based on Islamic canons. All banking activities must avoid interest, a concept that is forbidden in Islam. Instead, the bank earns profit (markup) and fees on the financing facilities that it extends to customers.

[edit] Banks in the economy

[edit] Size of global banking industry

Assets of the largest 1,000 banks in the world grew by 6.8% in the 2008/2009 financial year to a record $96.4 trillion while profits declined by 85% to $115bn. Growth in assets in adverse market conditions was largely a result of recapitalisation. EU banks held the largest share of the total, 56% in 2008/2009, down from 61% in the previous year. Asian banks' share increased from 12% to 14% during the year, while the share of US banks increased from 11% to 13%. Fee revenue generated by global investment banking totalled $66.3bn in 2009, up 12% on the previous year. [9]

The United States has the most banks in the world in terms of institutions (7,085 at the end of 2008) and possibly branches (82,000).[citation needed] This is an indicator of the geography and regulatory structure of the USA, resulting in a large number of small to medium-sized institutions in its banking system. As of Nov 2009, China's top 4 banks have in excess of 67,000 branches (ICBC:18000+, BOC:12000+,CCB:13000+,ABC:24000+) with an additional 140 smaller banks with an undetermined number of branches. Japan had 129 banks and 12,000 branches. In 2004, Germany, France, and Italy each had more than 30,000 branches—more than double the 15,000 branches in the UK.[9]

[edit] Bank crisis

Banks are susceptible to many forms of risk which have triggered occasional systemic crises. These include liquidity risk (where many depositors may request withdrawals beyond available funds), credit risk (the chance that those who owe money to the bank will not repay it), and interest rate risk (the possibility that the bank will become unprofitable, if rising interest rates force it to pay relatively more on its deposits than it receives on its loans).

Banking crises have developed many times throughout history, when one or more risks have materialized for a banking sector as a whole. Prominent examples include the bank run that occurred during the Great Depression, the U.S. Savings and Loan crisis in the 1980s and early 1990s, the Japanese banking crisis during the 1990s, and the subprime mortgage crisis in the 2000s. Usually, the governments bail out the bank through rescue plan or individual public intervention.[10]

[edit] Challenges within the banking industry

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[edit] United States

In the United States, the banking industry is a highly regulated industry with detailed and focused regulators. All banks with FDIC-insured deposits have the FDIC as a regulator; however, for examinations,[clarification needed] the Federal Reserve is the primary federal regulator for Fed-member state banks; the Office of the Comptroller of the Currency (“OCC”) is the primary federal regulator for national banks; and the Office of Thrift Supervision, or OTS, is the primary federal regulator for thrifts. State non-member banks are examined by the state agencies as well as the FDIC. National banks have one primary regulator—the OCC.

Each regulatory agency has their own set of rules and regulations to which banks and thrifts must adhere.

The Federal Financial Institutions Examination Council (FFIEC) was established in 1979 as a formal interagency body empowered to prescribe uniform principles, standards, and report forms for the federal examination of financial institutions. Although the FFIEC has resulted in a greater degree of regulatory consistency between the agencies, the rules and regulations are constantly changing.

In addition to changing regulations, changes in the industry have led to consolidations within the Federal Reserve, FDIC, OTS and OCC. Offices have been closed, supervisory regions have been merged, staff levels have been reduced and budgets have been cut. The remaining regulators face an increased burden with increased workload and more banks per regulator. While banks struggle to keep up with the changes in the regulatory environment, regulators struggle to manage their workload and effectively regulate their banks. The impact of these changes is that banks are receiving less hands-on assessment by the regulators, less time spent with each institution, and the potential for more problems slipping through the cracks, potentially resulting in an overall increase in bank failures across the United States.

The changing economic environment has a significant impact on banks and thrifts as they struggle to effectively manage their interest rate spread in the face of low rates on loans, rate competition for deposits and the general market changes, industry trends and economic fluctuations. It has been a challenge for banks to effectively set their growth strategies with the recent economic market. A rising interest rate environment may seem to help financial institutions, but the effect of the changes on consumers and businesses is not predictable and the challenge remains for banks to grow and effectively manage the spread to generate a return to their shareholders.

The management of the banks’ asset portfolios also remains a challenge in today’s economic environment. Loans are a bank’s primary asset category and when loan quality becomes suspect, the foundation of a bank is shaken to the core. While always an issue for banks, declining asset quality has become a big problem for financial institutions. There are several reasons for this, one of which is the lax attitude some banks have adopted because of the years of “good times.” The potential for this is exacerbated by the reduction in the regulatory oversight of banks and in some cases depth of management. Problems are more likely to go undetected, resulting in a significant impact on the bank when they are recognized. In addition, banks, like any business, struggle to cut costs and have consequently eliminated certain expenses, such as adequate employee training programs.

Banks also face a host of other challenges such as aging ownership groups. Across the country, many banks’ management teams and board of directors are aging. Banks also face ongoing pressure by shareholders, both public and private, to achieve earnings and growth projections. Regulators place added pressure on banks to manage the various categories of risk. Banking is also an extremely competitive industry. Competing in the financial services industry has become tougher with the entrance of such players as insurance agencies, credit unions, check cashing services, credit card companies, etc.

As a reaction, banks have developed their activities in financial instruments, through financial market operations such as brokerage and trading and become big players in such activities.

[edit] Brokered deposits

One source of deposits for banks is brokers who deposit large sums of money on the behalf of investors. This money will generally go to the banks which offer the most favorable terms, often better than those offered local depositors. It is possible for a bank to be engaged in business with no local deposits at all, all funds being brokered deposits. Accepting a significant quantity of such deposits, or "hot money" as it is sometimes called, puts a bank in a difficult and sometimes risky position, as the funds must be lend or invested in a way that yields a return sufficient to pay the high interest being paid on the brokered deposits. This may result in risky decisions and even in eventual failure of the bank. Banks which failed during 2008 and 2009 in the United States during the global financial crisis had, on average, four times more brokered deposits as a percent of their deposits than the average bank. Such deposits, combined with risky real estate investments, factored into the Savings and loan crisis of the 1980s. Regulation of brokered deposits is opposed by banks on the grounds that the practice can be a source of external funding to growing communities with insufficient local deposits.[11]

[edit] Profitability

A bank generates a profit from the differential between the level of interest it pays for deposits and other sources of funds, and the level of interest it charges in its lending activities. This difference is referred to as the spread between the cost of funds and the loan interest rate. Historically, profitability from lending activities has been cyclical and dependent on the needs and strengths of loan customers. In recent history, investors have demanded a more stable revenue stream and banks have therefore placed more emphasis on transaction fees, primarily loan fees but also including service charges on an array of deposit activities and ancillary services (international banking, foreign exchange, insurance, investments, wire transfers, etc.). Lending activities, however, still provide the bulk of a commercial bank's income.

In the past 20 years American banks have taken many measures to ensure that they remain profitable while responding to increasingly changing market conditions. First, this includes the Gramm-Leach-Bliley Act, which allows banks again to merge with investment and insurance houses. Merging banking, investment, and insurance functions allows traditional banks to respond to increasing consumer demands for "one-stop shopping" by enabling cross-selling of products (which, the banks hope, will also increase profitability). Second, they have expanded the use of risk-based pricing from business lending to consumer lending, which means charging higher interest rates to those customers that are considered to be a higher credit risk and thus increased chance of default on loans. This helps to offset the losses from bad loans, lowers the price of loans to those who have better credit histories, and offers credit products to high risk customers who would otherwise been denied credit. Third, they have sought to increase the methods of payment processing available to the general public and business clients. These products include debit cards, prepaid cards, smart cards, and credit cards. They make it easier for consumers to conveniently make transactions and smooth their consumption over time (in some countries with underdeveloped financial systems, it is still common to deal strictly in cash, including carrying suitcases filled with cash to purchase a home). However, with convenience of easy credit, there is also increased risk that consumers will mismanage their financial resources and accumulate excessive debt. Banks make money from card products through interest payments and fees charged to consumers and transaction fees to companies that accept the cards. Helps in making profit and economic development as a whole.





Saturday, 6 March 2010

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

Although mechanical examples of computers have existed through much of recorded human history, the first electronic computers were developed in the mid-20th century (1940–1945). These 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 small pocket 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". The embedded computers found in many devices from MP3 players to fighter aircraft and from toys to industrial robots are however the most numerous.

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 certain minimum capability is, in principle, capable of performing the same tasks that any other computer can perform. Therefore computers ranging from a netbook to a supercomputer are all able to perform the same computational tasks, given enough time and storage capacity.

Contents

[hide]

story of computing

Main article: History of computing hardware

http://bits.wikimedia.org/skins-1.5/common/images/magnify-clip.png

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

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 to be used in that sense until the middle of the 20th century. From the end of the 19th century onwards though, the word began to take on its more familiar meaning, describing a machine that carries out computations.[3]

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 (which dates from about 150–100 BC). 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.[4] 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.[5] 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,[6][7] 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.[5]

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.

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.

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.[8] Limited finances and Babbage's inability to resist tinkering with the design meant that the device was never completed.

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 ..."[9] 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. Of his role in 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".[10]

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.[11]

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.[12]

Defining characteristics of some early digital computers of the 1940s (In the history of computing hardware)

Name

First operational

Numeral system

Computing mechanism

Programming

Turing complete

Zuse Z3 (Germany)

May 1941

Binary

Electro-mechanical

Program-controlled by punched film stock (but no conditional branch)

Yes (1998)

Atanasoff–Berry Computer (US)

1942

Binary

Electronic

Not programmable—single purpose

No

Colossus Mark 1 (UK)

February 1944

Binary

Electronic

Program-controlled by patch cables and switches

No

Harvard Mark I – IBM ASCC (US)

May 1944

Decimal

Electro-mechanical

Program-controlled by 24-channel punched paper tape (but no conditional branch)

No

Colossus Mark 2 (UK)

June 1944

Binary

Electronic

Program-controlled by patch cables and switches

No

ENIAC (US)

July 1946

Decimal

Electronic

Program-controlled by patch cables and switches

Yes

Manchester Small-Scale Experimental Machine (Baby) (UK)

June 1948

Binary

Electronic

Stored-program in Williams cathode ray tube memory

Yes

Modified ENIAC (US)

September 1948

Decimal

Electronic

Program-controlled by patch cables and switches plus a primitive read-only stored programming mechanism using the Function Tables as program ROM

Yes

EDSAC (UK)

May 1949

Binary

Electronic

Stored-program in mercury delay line memory

Yes

Manchester Mark 1 (UK)

October 1949

Binary

Electronic

Stored-program in Williams cathode ray tube memory and magnetic drum memory

Yes

CSIRAC (Australia)

November 1949

Binary

Electronic

Stored-program in mercury delay line memory

Yes

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:

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

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

  • 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.[13]
  • The non-programmable Atanasoff–Berry Computer (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 then 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),[14] 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.
  • 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.

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 to be demonstrated working was the Manchester Small-Scale Experimental Machine (SSEM or "Baby"), while the EDSAC, completed a year after SSEM, was the first practical implementation of the stored program design. 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.

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.[15] 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].

Stored program architecture

Main articles: Computer program and Computer programming

The defining feature of modern computers which distinguishes them from all other machines is that they can be programmed. That is to say that a list of instructions (the program) can be given to the computer and it will store them and carry them out at some time in the future.

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.[16]

However, computers cannot "think" for themselves in the sense that they only solve problems in exactly the way they are programmed to. An intelligent human faced with the above addition task might soon realize that instead of actually adding up all the numbers one can simply use the equation

1+2+3+...+n = {{n(n+1)} \over 2}

and arrive at the correct answer (500,500) with little work.[17] In other words, a computer programmed to add up the numbers one by one as in the example above would do exactly that without regard to efficiency or alternative solutions.

Programs

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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.

In practical terms, a computer program may run from just a few instructions to many millions of instructions, as in a program for a word processor or a web browser. A typical modern computer can execute billions of instructions per second (gigahertz or GHz) and rarely make 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.

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 may be harnessed for malicious intent by an unscrupulous user writing an "exploit"—code designed to take advantage of a bug and disrupt a program'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.[18]

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 instructions) can be represented as lists of numbers and can themselves be manipulated inside the computer just as if they were 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 this technique was used with many early computers,[19] it is extremely tedious 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.[20]

Though considerably easier than in machine language, writing long programs in assembly language is often difficult and error prone. Therefore, most complicated 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.[21] Since high level languages are more abstract than assembly language, it is 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.

Example

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A traffic light showing red

Suppose a computer is being employed to operate a traffic light at an intersection between two streets. The computer has the following three basic instructions.

1. ON(Streetname, Color) Turns the light on Streetname with a specified Color on.

2. OFF(Streetname, Color) Turns the light on Streetname with a specified Color off.

3. WAIT(Seconds) Waits a specifed number of seconds.

4. START Starts the program

5. REPEAT Tells the computer to repeat a specified part of the program in a loop.

Comments are marked with a // on the left margin. Comments in a computer program do not affect the operation of the program. They are not evaluated by the computer. Assume the streetnames are Broadway and Main.

START

//Let Broadway traffic go

OFF(Broadway, Red)

ON(Broadway, Green)

WAIT(60 seconds)

//Stop Broadway traffic

OFF(Broadway, Green)

ON(Broadway, Yellow)

WAIT(3 seconds)

OFF(Broadway, Yellow)

ON(Broadway, Red)

//Let Main traffic go

OFF(Main, Red)

ON(Main, Green)

WAIT(60 seconds)

//Stop Main traffic

OFF(Main, Green)

ON(Main, Yellow)

WAIT(3 seconds)

OFF(Main, Yellow)

ON(Main, Red)

//Tell computer to continuously repeat the program.

REPEAT ALL

With this set of instructions, the computer would cycle the light continually through red, green, yellow and back to red again on both streets.

However, suppose there is a simple on/off switch connected to the computer that is intended to be used to make the light flash red while some maintenance operation is being performed. The program might then instruct the computer to:

START

IF Switch == OFF then: //Normal traffic signal operation

{

//Let Broadway traffic go

OFF(Broadway, Red)

ON(Broadway, Green)

WAIT(60 seconds)

//Stop Broadway traffic

OFF(Broadway, Green)

ON(Broadway, Yellow)

WAIT(3 seconds)

OFF(Broadway, Yellow)

ON(Broadway, Red)

//Let Main traffic go

OFF(Main, Red)

ON(Main, Green)

WAIT(60 seconds)

//Stop Main traffic

OFF(Main, Green)

ON(Main, Yellow)

WAIT(3 seconds)

OFF(Main, Yellow)

ON(Main, Red)

//Tell the computer to repeat this section continuously.

REPEAT THIS SECTION

}

IF Switch == ON THEN: //Maintenance Mode

{

//Turn the red lights on and wait 1 second.

ON(Broadway, Red)

ON(Main, Red)

WAIT(1 second)

//Turn the red lights off and wait 1 second.

OFF(Broadway, Red)

OFF(Main, Red)

WAIT(1 second)

//Tell the computer to repeat the statements in this section.

REPEAT THIS SECTION

}

In this manner, the traffic signal will run a flash-red program when the switch is on, and will run the normal program when the switch is off. Both of these program examples show the basic layout of a computer program in a simple, familiar context of a traffic signal. Any experienced programmer can spot many software bugs in the program, for instance, not making sure that the green light is off when the switch is set to flash red. However, to remove all possible bugs would make this program much longer and more complicated, and would be confusing to nontechnical readers: the aim of this example is a simple demonstration of how computer instructions are laid out.

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

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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.[22] 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.[23]

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.[24]

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.[25] 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

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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.[26]

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

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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.[27] Devices that provide input or output to the computer are called peripherals.[28] 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.[29]

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.[30]

Before the era of cheap computers, the principle 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

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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.[31] 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

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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.[32]

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.[33] 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.

Further topics

Hardware

Main article: Personal computer 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[34]

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, Windows CE

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

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

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, 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, ACM Special Interest Groups, IET, IFIP, BCS

Free/Open source software groups

Free Software Foundation, Mozilla Foundation, Apache Software Foundation

See also

Information technology portal



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

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

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

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

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

9. ^ Columbia University Computing History: Herman Hollerith

10. ^ "Alan Turing - Time 100 People of the Century". Time Magazine. http://www.yachtingnet.com/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"

11. ^ Spiegel: The inventor of the computer's biography was published

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

13. ^ 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.

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

15. ^ Lavington 1998, p. 37

16. ^ 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)

17. ^ Attempts are often made to create programs that can overcome this fundamental limitation of computers. Software that mimics learning and adaptation is part of artificial intelligence.

18. ^ 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.

19. ^ 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.

20. ^ 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.

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

22. ^ 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.

23. ^ 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.

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

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

26. ^ 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 1988)

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

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

29. ^ 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.

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

31. ^ 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)

32. ^ 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..."

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

34. ^ 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.

· a 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.

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

· a 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.

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