Computer in Nepal

Laptop Computer

2009-11-04T22:09:00.000-08:00

A laptop is a personal computer designed for mobile use and small and light enough to sit on one's lap while in use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device , speakers, and often including a battery, into a single small and light unit. The rechargeable battery is charged from an AC adapter and typically stores enough energy to run the laptop for two to three hours in its initial state, depending on the configuration and power management of the computer.
Laptops are usually shaped like a large notebook with thicknesses between 0.7–1.5 inches and dimensions ranging from 10x8 inches to 15x11 inches and up. Modern laptops weigh 3 to 12 pounds; older laptops were usually heavier. Most laptops are designed in the flip form factor to protect the screen and the keyboard when closed. Modern tablet laptops have a complex joint between the keyboard housing and the display, permitting the display panel to swivel and then lie flat on the keyboard housing. They usually have a touchscreen display and some include handwriting recognition or graphics drawing capability.
Laptops were originally considered to be "a small niche market" and were thought suitable mostly for "specialized field applications" such as "the military, the Internal Revenue Service, accountants and sales representatives". But today, there are already more laptops than desktops in businesses, and laptops are becoming obligatory for student use and more popular for general use. In 2008 more laptops than desktops were sold in the US and it has been predicted that the same milestone will be reached in the worldwide market as soon as late 2009.

Hisdtory of Dell

2009-11-04T21:55:00.000-08:00

While a student at the University of Texas at Austin in 1984, Michael Dell founded the company as PC's Limited with capital of $1000.Operating from Michael Dell's off-campus dormitory room at Dobie Center, the startup aimed to sell IBM PC-compatible computers built from stock components. Michael Dell started trading in the belief that by selling personal computer-systems directly to customers, PC's Limited could better understand customers' needs and provide the most effective computing solutions to meet those needs.[citation needed] Michael Dell dropped out of school in order to focus full-time on his fledgling business, after getting about $300,000 in expansion-capital from his family.
In 1985, the company produced the first computer of its own design — the "Turbo PC", sold for US$795 — which contained an Intel 8088-compatible processor running at a speed of 8 MHz. PC's Limited advertised the systems in national computer-magazines for sale directly to consumers, and custom-assembled each ordered unit according to a selection of options. This offered buyers prices lower than those of retail brands, but with greater convenience than assembling the components themselves. Although not the first company to use this model, PC's Limited became one of the first to succeed with it. The company grossed more than $73 million in its first year of trading.

The company changed its name to "Dell Computer Corporation" in 1988. In 1989, Dell Computer set up its first on-site-service programs in order to compensate for the lack of local retailers prepared to act as service centers. Also in 1987, the company set up its first operations in Ireland; eleven more international operations followed within the next four years. In June 1988, Dell's market capitalization grew by $30 million to $80 million from its June 22 initial public offering of 3.5 million shares at $8.50 a share. In 1990, Dell Computer Corporation tried selling its products indirectly through warehouse clubs and computer superstores, but met with little success, and the company re-focused on its more successful direct-to-consumer sales model. In 1992, Fortune magazine included Dell Computer Corporation in its list of the world's 500 largest companies.
In 1996, Dell began selling computers via its web site.
In 2002, Dell attempted to expand by tapping into the multimedia and home-entertainment markets with the introduction of televisions, handhelds, and digital audio players. Dell has also produced Dell-brand printers for home and small-office use.
In 2003, at the annual company meeting, the stockholders approved changing the company name to "Dell Inc." to recognize the company's expansion beyond computers.
In 2004, the company announced that it would build a new assembly-plant near Winston-Salem, North Carolina; the city and county provided Dell with $37.2 million in incentive packages; the state provided approximately $250 million in incentives and tax breaks. In July, Michael Dell stepped aside as Chief Executive Officer while retaining his position as Chairman of the Board. Kevin Rollins, who had held a number of executive posts at Dell, became the new CEO.

In 2005, the share of sales coming from international markets increased, as revealed in the company's press releases for the first two quarters of its fiscal 2005 year. In February 2005 Dell appeared in first place in a ranking of the "Most Admired Companies" published by Fortune magazine. In November 2005 BusinessWeek magazine published an article titled "It's Bad to Worse at Dell" about shortfalls in projected earnings and sales, with a worse-than-predicted third-quarter financial performance — a bad omen for a company that had routinely underestimated its earnings. Dell acknowledged that faulty capacitors on the motherboards of the Optiplex GX270 and GX280 had already cost the company $300 million. The CEO, Kevin Rollins, attributed the bad performance partially to Dell's focus on low-end PCs.
In 2006, Dell purchased the computer hardware manufacturer Alienware. Dell Inc.'s plan anticipated Alienware continuing to operate independently under its existing management. Alienware expected to benefit from Dell's efficient manufacturing system.On January 31, 2007, Kevin B. Rollins, CEO of the company since 2004, resigned as both CEO and as a director, and Michael Dell resumed his former role as CEO. Investors and many shareholders had called for Rollins' resignation because of poor company performance. At the same time, the company announced that, for the fourth time in five quarters, earnings would fail to reach consensus analyst-estimates.
In February 2007 Dell became the subject of formal investigations by the US SEC and the U.S. Attorney for the Southern District of New York. The company has not formally filed financial reports for either the third or fourth fiscal quarter of 2006, and several class-action lawsuits have arisen in the wake of its recent financial performance. Dell Inc's lack of formal financial disclosure would normally subject the company to de-listing from the NASDAQ, but the exchange has granted Dell a waiver, allowing the stock to trade normally.On March 1, 2007, the company issued a preliminary quarterly earnings report which showed gross sales of $14.4 billion, down 5% year-over-year, and net income of $687 million, down 33%. Net earnings would have declined even more if not for the effects of eliminated employee bonuses, which accounted for six cents per share. NASDAQ extended the company's deadline for filing financials to May 4.

Desktop Computer

2009-11-04T21:37:00.000-08:00

A desktop computer is a personal computer (PC) in a form intended for regular use at a single location, as opposed to a mobile laptop or portable computer. Prior to the wide spread of microprocessors, a computer that could fit on a desk was considered remarkably small. Desktop computers come in a variety of types ranging from large vertical tower cases to small form factor models that can be tucked behind an LCD monitor. "Desktop" can also indicate a horizontally-oriented computer case usually intended to have the display screen placed on top to save space on the desk top. Most modern desktop computers have separate screens and keyboards. Tower cases are desktop cases in the former sense, though not in the latter. Cases intended for home theater PC systems are usually considered to be desktop cases in both senses, regardless of orientation and placement.

History :Early computers took the space of a room. Minicomputers generally fit into one or a few refrigerator sized racks. It was not until the 1970s when computers such as the HP 9800 series desktop computers were fully programmable computers that fit entirely on top of a desk. The first large calculators were introduced in 1971, leading to a model programmable in BASIC in 1972. They used used smaller version of a minicomputer design based on ROM memory and had small one-line LED alphanumeric displays. They could draw computer graphics with a plotter. The Wang 2200 of 1973 had a full-size CRT and cassette tape storage. The IBM 5100 in 1975 had a small CRT display and could be programmed in BASIC and APL. These were generally expensive specialized computers sold for business or scientific uses. By the late 1970s and 1980s personal computers such as the Apple II series and the IBM Personal Computer used standard processors to reduce cost to put a complete computer on top of a desk with a separate monitor. These would find uses in the home as well as in business and industry, and later incorporate graphic user interfaces and powerful networked operating systems such as Mac and Windows.

All-in-One : All-in-One computers are desktop computers that combine the monitor into the same case as the CPU. Apple has manufactured several popular examples of all-in-one computers, such as the original Macintosh of the mid-1980s and the iMac of the late 1990s and 2000s. Some older 8-bit computers, such as the Commodore PET 2001 or Kaypro II, also fit into this category. All-in-One PCs are typically more portable than other desktop PCs and many have been built with carrying handles integrated into the case. They can simply be unplugged and transported to a new location.
Like laptops, All-in-One desktop computers are characterized by a comparative lack of upgradeability or hardware customization, as internal hardware is often placed in the back of the visual display unit. Furthermore, in the case of the iMac line since 2002, the CPU and other internal hardware units are, more or less, permanently glued to the motherboard due to space constraints.
However, latest models of the All In One Computer have changed their approach this issue. Many of the current offerings, like the Handii myFace and others, are using standard off-the-shelf components and are designing upgrade convenience into their products.

History of Computers

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The development of the modern day computer was the result of advances in technologies and man's need to quantify. Papyrus helped early man to record language and numbers. The abacus was one of the first counting machines. Some of the earlier mechanical counting machines lacked the technology to make the design work. For instance, some had parts made of wood prior to metal manipulation and manufacturing.

Imagine the wear on wooden gears.

This history of computers site includes the names of early pioneers of math and computing and links to related sites about the History of Computers, for further study. This site would be a good Web adjunct to accompany any book on the History of Computers or Introduction to Computers. The "H" Section includes a link to the History of the Web Beginning at CERN which includes Bibliography and Related Links. Hitmill.com strives to always include related links for a broader educational experience.

My Computer

2009-11-04T21:21:00.000-08:00

A section of Microsoft Windows that was introduced with the release of Microsoft Windows 95 and included with all versions of Windows after that. My Computer allows the user to explore the contents of their computer drives as well as manage their computer files. To the right, the top image is an example of the My Computer icon in Microsoft Windows XP. With the introduction of Windows Vista, Microsoft changed the traditional My Computer icon to Computer, the bottom image to the right is an example of what this icon looks like. Although the name has changed this icon still acts identical to the earlier My Computer.

Wikipedia history

2009-11-04T21:17:00.000-08:00

The wikipedia.org website, Wikipedia's homepage for all languages
Wikipedia was founded as an offshoot of Nupedia, a now-abandoned project to produce a free encyclopedia. Nupedia had an elaborate system of peer review and required highly qualified contributors, but the writing of articles was slow. During 2000, Jimmy Wales, founder of Nupedia, and Larry Sanger, whom Wales had employed to work on the project, discussed ways of supplementing Nupedia with a more open, complementary project. Multiple sources suggested the idea that a wiki might allow members of the public to contribute material, and Nupedia's first wiki went online on January 10, 2001.
There was considerable resistance on the part of Nupedia's editors and reviewers to the idea of associating Nupedia with a Web site in the wiki format, so the new project was given the name "Wikipedia" and launched on its own domain, wikipedia.com, on January . The bandwidth and server were donated by Wales. Other current and past Bomis employees who have worked on the project include Tim Shell, one of the cofounders of Bomis and its current CEO, and programmer Jason Richey. The domain was eventually changed to the present wikipedia.org when the not-for-profit Wikimedia Foundation was launched as its new parent organization, prompting the use of a ".org" domain to denote its non-commercial nature. In March 2007, the word wiki became a newly recognized English word.In May 2001, a wave of non-English Wikipedias was launched—in Catalan, Chinese, Dutch, Esperanto, French, German, Hebrew, Italian, Japanese, Portuguese, Russian, Spanish, and Swedish. These were soon joined by Arabic and Hungarian. In September, Polish was added, and further commitment to the multilingual provision of Wikipedia was made. At the end of the year, Afrikaans, Norwegian, and Serbocroatian versions were announced

Wikipedia

2009-11-04T21:04:00.000-08:00

The name "Wikipedia" is a portmanteau of the words wiki and encyclopedia. Wikipedia's articles provide links to guide the user to related pages with additional information.
Wikipedia is written collaboratively by an international group of volunteers. Anyone with internet access can write and make changes to Wikipedia articles. There are no requirements to provide one's real name when contributing; rather, each writer's privacy is protected unless they choose to reveal their identity themselves. Since its creation in 2001, Wikipedia has grown rapidly into one of the largest reference web sites, attracting around 65 million visitors monthly as of 2009. There are more than 75,000 active contributors working on more than 14,000,000 articles in more than 260 languages. As of today, there are 3,085,148 articles in English. Every day, hundreds of thousands of visitors from around the world collectively make tens of thousands of edits and create thousands of new articles to augment the knowledge held by the Wikipedia encyclopedia.

Visitors do not need specialized qualifications to contribute. Wikipedia's intent is to have articles that cover existing knowledge, not create new knowledge . This means that people of all ages and cultural and social backgrounds can write Wikipedia articles. Most of the articles can be edited by anyone with access to the Internet, simply by clicking the edit this page link. Anyone is welcome to add information, cross-references, or citations, as long as they do so within Wikipedia's editing policies and to an appropriate standard. Substandard or disputed information is subject to removal. Users need not worry about accidentally damaging Wikipedia when adding or improving information, as other editors are always around to advise or correct obvious errors, and Wikipedia's software is carefully designed to allow easy reversal of editorial mistakes.
Because Wikipedia is an ongoing work to which, in principle, anybody can contribute, it differs from a paper-based reference source in important ways. In particular, older articles tend to be more comprehensive and balanced, while newer articles more frequently contain significant misinformation, unencyclopedic content, or vandalism. Users need to be aware of this to obtain valid information and avoid misinformation that has been recently added and not yet removed .

However, unlike a paper reference source, Wikipedia is continually updated, with the creation or updating of articles on topical events within seconds, minutes, or hours, rather than months or years for printed encyclopedias. What Wikipedia is will give an understanding of how to consult or contribute to Wikipedia. Further information on key topics appears below. Further advice is at Frequently asked questions, advice for parents, or see Where to ask questions. For help with editing and other issues, see Help:Contents.

Computer multitasking

2009-11-04T20:55:00.000-08:00

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.

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.

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.

Tablet PC

2009-11-04T00:03:00.000-08:00

HP Compaq tablet PC with rotating/removable keyboard.
A tablet PC is a notebook or slate-shaped mobile computer, first introduced by Pen computing in the early 90s with their PenGo Tablet Computer and popularized by Microsoft. Its touchscreen or graphics tablet/screen hybrid technology allows the user to operate the computer with a stylus or digital pen, or a fingertip, instead of a keyboard or mouse. The form factor offers a more mobile way to interact with a computer. Tablet PCs are often used where normal notebooks are impractical or unwieldy, or do not provide the needed functionality.
As technology and functionality continue to progress, prototype tablet PC's will continue to emerge. The Microsoft Courier, a personal business device, has two 7" monitors that support multi-touch gestures, Wi-Fi capabilities and has a built-in camera. The device looks to be a replacement to traditional planners while offering what most digital planners cannot, two pages and large writing spaces.

Netbooks

2009-11-03T23:58:00.000-08:00

Netbooks are small portable computers in a "clamshell" design, that are designed specifically for wireless communication and access to the Internet. They are generally much lighter and cheaper than subnotebooks, and have a smaller display, between 7" and 9", with a screen resolution between 800x600 and 1024x768 but newer models feature higher resolution at up to 1280x768 like the Gigabyte M912X netbook. The operating systems and applications on them are usually specially modified so they can be comfortably used with a smaller sized screen, and the OS was in the start Linux, although most netbooks run one of the NT version, Windows XP or Windows Vista (For example Sony's Tablet Netbook). Netbooks Have built in Wireless connectivity.Some even have smaller but faster solid state storage systems instead of mechanical hard-disks. Storage capacities were usually in the 4 to 16 GB for solid state flash drives range but have largely increased with mechanical drives, expanding up to 160GB for example the Gigabyte M912X and the MSI WInd U100 with units that have mechanical hard drives instead of solid state flash drives. One of the first examples of such a system was the original Eee PC.
The emergence of new market segment of small, energy-efficient and low-cost devices designed for access to the Internet could threaten established companies like Microsoft, Intel, HP or Dell, analysts said in July 2008. A market research firm International Data Corporation predicted that the category could grow from fewer than 500,000 in 2007 to 9 million in 2012 as the market for low cost and secondhand computers expands in developed economies. Also, after Microsoft ceased selling consumer versions of Windows XP, it made an exception and continued to offer the operating system for netbook and nettop makers.

Laptop

2009-11-03T23:55:00.000-08:00

A laptop computer or simply laptop, also called a notebook computer or sometimes a notebook, is a small personal computer designed for portability. Usually all of the interface hardware needed to operate the laptop, such as parallel and serial ports, graphics card, sound channel, etc., are built in to a single unit. Laptops contain high capacity batteries that can power the device for extensive periods of time, enhancing portability. Once the battery charge is depleted, it will have to be recharged through a power outlet. In the interest of saving power, weight and space, they usually share RAM with the video channel, slowing their performance compared to an equivalent desktop machine.
One main drawback of the laptop is that, due to the size and configuration of components, relatively little can be done to upgrade the overall computer from its original design. Some devices can be attached externally through ports (including via USB), however internal upgrades are not recommended or in some cases impossible, making the desktop PC more modular.
A subtype of notebooks, called subnotebooks, are computers with most of the features of a standard laptop computer but smaller. They are larger than hand-held computers, and usually run full versions of desktop/laptop operating systems. Ultra-Mobile PCs (UMPC) are usually considered subnotebooks, or more specifically, subnotebook Tablet PCs (see below). Netbooks are sometimes considered in this category, though they are sometimes separated in a category of their own (see below).
Desktop replacements, meanwhile, are large laptops meant to replace a desktop computer while keeping the mobility of a laptop.

2009-11-03T23:53:00.000-08:00

Prior to the wide spread of PCs a computer that could fit on a desk was considered remarkably small. Today the phrase usually indicates a particular style of computer case. Desktop computers come in a variety of styles ranging from large vertical tower cases to small form factor models that can be tucked behind an LCD monitor. In this sense, the term 'desktop' refers specifically to a hoarizontally-oriented case, usually intended to have the display screen placed on top to save space on the desk top. Most modern desktop computers have separate screens and keyboards.

ppp.cccc

2009-11-03T23:33:00.000-08:00

The capabilities of the personal computer have changed greatly since the introduction of electronic computers. By the early 1970s, people in academic or research institutions had the opportunity for single-person use of a computer system in interactive mode for extended durations, although these systems would still have been too expensive to be owned by a single person. The introduction of the microprocessor, a single chip with all the circuitry that formerly occupied large cabinets, led to the proliferation of personal computers after about 1975. In what was later to be called The Mother of All Demos, SRI researcher Douglas Englebart in 1968 gave a preview of what would become the staples of daily working life in the 21st century - e-mail, hypertext, word processing, video conferencing, and the mouse.

Early personal computers - generally called microcomputers - were sold often in Electronic kit form and in limited volumes, and were of interest mostly to hobbyists and technicians. Minimal programming was done by toggle switches, and output was provided by front panel indicators. Practical use required peripherals such as keyboards, computer terminals, disk drives, and printers. Micral N was the earliest commercial, non-kit "personal" computer based on a microprocessor, the Intel 8008. It was built starting in 1972 and about 90,000 units were sold. Unlike other hobbyist computers of its day, which were sold as electronics kits, in 1976 Steve Jobs and Steve Wozniak sold the Apple I computer circuit board, which was fully prepared and contained about 30 chips. The first complete personal computer was the Commodore PET introduced in January 1977. It was soon followed by the popular Apple II. Mass-market pre-assembled computers allowed a wider range of people to use computers, focusing more on software applications and less on development of the processor hardware.

Throughout the late 1970s and into the 1980s, computers were developed for household use, offering personal productivity, programming and games. Somewhat larger and more expensive systems (although still low-cost compared with minicomputers and mainframes) were aimed for office and small business use. Workstations are characterized by high-performance processors and graphics displays, with large local disk storage, networking capability, and running under a multitasking operating system. Workstations are still used for tasks such as computer-aided design, drafting and modelling, computation-intensive scientific and engineering calculations, image processing, architectural modelling, and computer graphics for animation and motion picture visual effects.

Eventually due to the IBM-PC's influence on the Personal Computer market Personal Computers and Home Computers lost any technical distinction. Business computers acquired color graphics capability and sound, and home computers and game systems users used the same processors and operating systems as office workers. Mass-market computers had graphics capabilities and memory comparable to dedicated workstations of a few years before. Even local area networking, originally a way to allow business computers to share expensive mass storage and peripherals, became a standard feature of the personal computers used at home.

Personal Computer

2009-11-03T23:16:00.000-08:00

A personal computer (PC) is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end user, with no intervening computer operator. This is in contrast to the batch processing or time-sharing models which allowed large expensive mainframe systems to be used by many people, usually at the same time, or large data processing systems which required a full-time staff to operate efficiently.
A personal computer may be a desktop computer, a laptop, tablet PC or a handheld PC (also called palmtop). The most common microprocessors are x86-compatible CPUs, ARM architecture CPUs and PowerPC CPUs. Software applications for personal computers include word processing, spreadsheets, databases, Web browsers and e-mail clients, games, and myriad personal productivity and special-purpose software. Modern personal computers often have high-speed or dial-up connections to the Internet, allowing access to the World Wide Web and a wide range of other resources.
A PC may be used at home, or may be found in an office. Personal computers can be connected to a local area network (LAN) either by a cable or wirelessly.
While early PC owners usually had to write their own programs to do anything useful with the machines, today's users have access to a wide range of commercial and non-commercial software which is provided in ready-to-run form. Since the 1980s, Microsoft and Intel have dominated much of the personal computer market with the Wintel platform.

Computer memory

2009-11-03T23:13:00.000-08:00

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.Each byte is able to represent 256 different numbers; 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.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.

Computer Function

2009-11-03T23:10:00.000-08:00

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.

Computer Program

2009-11-03T23:06:00.000-08:00

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 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 and this technique was used with many early computers, 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 tend to be unique to a particular type of computer. For instance, an ARM architecture computer cannot understand the machine language of an Intel Pentium or the AMD Athlon 64 computer that might be in a PC.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.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.

Stored program architecture

2009-11-03T23:04:00.000-08:00

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 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 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 . 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:

History of Computer

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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.
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 mec. Hero of Alexandria 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. 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. 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, 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.
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. 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 ..." 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 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."
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.
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" , which was the first to use binary circuits to perform an arithmetic operation. Later models added greater sophistication including complex

COMPUTER

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A computer is a machine that manipulates data according to a set of instructions.
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). 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. Simple computers are small enough to fit into a wristwatch, and can be powered by a watch 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 mobile phone to a supercomputer are all able to perform the same computational tasks, given enough time and storage capacity.