Personal computer

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A personal computer (PC) is a computer whose original sales price, size, and capabilities make it useful for individuals.

A personal computer may be a home computer, or may be found in an office, often connected to a local area network. The distinguishing characteristic is that the computer is used only (or mostly) by one person at a time, in a very interactive fashion, with no significant delay between an operator action and response by the computer. This is opposite to the batch processing or time-sharing models which allowed large expensive systems to be used by many people, usually at the same time.

The capabilities of a 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 individual. The introduction of the microprocessor, a single chip with all the circuitry that formerly occupied large cabinets, lead to the proliferation of personal computers after about 1975. Early personal computers generally called microcomputers, sold often in kit form and in limited volumes and were of interest mostly to hobbyists and technicians. By the late 1970s, 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 1970s and 1980s, home computers were developed for household use, offering some personal productivity, programming and games, while somewhat larger and more expensive systems (although still low-cost compared with minicomputers and mainframes) were aimed for office and small business use.

Eventually the market segments lost any technical distinction; business computers acquired color graphics capacity and sound, and home computers and game systems used the same processors and operating systems as office-bound computers. Even local area networking, originally a way to allow business computers to share expensive mass storage and peripherals, became a standard feature of a home computer.

Today a personal computer may be a desktop computer, a laptop computer, or a tablet computer. The most common operating systems are Microsoft Windows, Mac OS and Linux, while the most common microprocessors are the x86 and PowerPC CPUs. Software applications for personal computers include word processing, spreadsheets, games, and a myriad of 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. While early personal computer 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 free software which is easily installed. The coming convergence^[1] between larger devices and the Personal Digital Assistants (PDAs), mobile phone and wearable computer markets which have similar functions, operating systems and even the same components, will decide if personal computer will refer to these devices.^[2][3][4].

[edit] Etymology

It is unknown who coined the phrase with the intent of a small affordable computing device but John W. Mauchly described such a device in a November 3, 1962 New York Times article entitled "Pocket Computer may replace Shopping List". Six years later a manufacturer took a risk at referring to their product this way when Hewlett Packard advertised their "Powerful Computing Genie" as "The New Hewlett Packard 9100A personal computer".^[5] This advertisement was too extreme for the target audience and replaced with a much drier ad for the HP 9100A programmable calculator.^[6] During the next 7 years the phrase had gained usage so when Byte magazine, published its first edition it referred to its readers as being in the "personal computing field",^[7] while Creative Computing defined the personal computer as a "non-(time)shared system containing sufficient processing power and storage capabilities to satisfy the needs of an individual user." ^[8] Two years later when the 1977 Trinity of preassembled small computers hit the markets, the Apple II^[9] and the PET 2001^[10] were advertised as 'personal computers', while the TRS-80 was a microcomputer used for household tasks including "personal financial management". By 1979 over half a million microcomputers were sold and the youth of the day had a new concept of the personal computer.^[11]

On January 3 1983, the Personal Computer was the first non-human to be announced as Person of the Year by Time Magazine, in 1982.^[12]

Today, "PC" is frequently used to indicate only personal computers based on the AT/ATX architectures in order to distinguish them from Apples Mac computers. They are capable of running a range of of operating systems.

[edit] History

Main article: History of computing hardware (1960s-present)

[edit] Mainframes and large minicomputers

Before the introduction of the microprocessor in the early 1970s, computers were generally large, costly systems owned by large corporations, universities, government agencies, and similar-sized institutions. End users often did not directly interact with the machine, but instead would prepare tasks for the computer on off-line equipment, such as card punches. A number of assignments for the computer would be gathered up and processed in batch mode. After the job had completed, users could collect the results. In some cases it could take hours or days between submitting a job to the computing center and receiving the output.

A more interactive form of computer use developed commercially by the middle 1960s. In a time-sharing system, multiple computer terminals let many people share the use of one mainframe computer processor. This was common in business applications and in science and engineering.

A different model of computer use was foreshadowed by the way in which early, pre-commercial, experimental computers were used, where one user had exclusive use of a processor. Some of the first computers that might be called "personal" were early minicomputers such as the LINC and PDP-8, and later on VAX and larger minicomputers from Digital Equipment Corporation (DEC), Data General, Prime Computer, and others. By today's standards they were very large (about the size of a refrigerator) and cost prohibitive (typically tens of thousands of US dollars), and thus were rarely purchased by an individual. However, they were much smaller, less expensive, and generally simpler to operate than many of the mainframe computers of the time. Therefore, they were accessible for individual laboratories and research projects. Minicomputers largely freed these organizations from the batch processing and bureaucracy of a commercial or university computing center.

In addition, minicomputers were relatively interactive and soon had their own operating systems. The minicomputer Xerox Alto (1973) was a landmark step in the development of personal computers, because of its graphical user interface, bit-mapped high resolution screen, large internal and external memory storage, mouse, and special software. ^[13]

[edit] Computers at home

One early use of the term "personal computer" appeared in a November 3, 1962, New York Times article reporting John W. Mauchly's vision of future computing as detailed at a recent meeting of the American Institute of Industrial Engineers. Mauchly stated, "There is no reason to suppose the average boy or girl cannot be master of a personal computer.^[14]"

The minicomputer ancestors of the modern personal computer used early integrated circuit (microchip) technology, which reduced size and cost, but they contained no microprocessor. This meant that they were still large and difficult to manufacture just like their mainframe predecessors. After the "computer-on-a-chip" was commercialized, the cost to manufacture a computer system dropped dramatically. The arithmetic, logic, and control functions that previously occupied several costly circuit boards were now available in one integrated circuit, making it possible to produce them in high volume. Concurrently, advances in the development of solid state memory eliminated the bulky, costly, and power-hungry magnetic core memory used in prior generations of computers.

There were a few researchers at places such as SRI and Xerox PARC who were working on computers that a single person could use and could be connected by fast, versatile networks: not home computers, but personal ones.

[edit] Kenbak-1

Main article: Kenbak-1

The Kenbak-1 is considered by the Computer History Museum to be the world's first ever personal computer (however, the Datapoint 2200 may have been invented first, sold first, or both; the exact dates have not been established). Little information is recorded regarding the Kenbak-1, as around only 40 machines were ever built and sold.

[edit] Datapoint 2200

Main article: Datapoint 2200

A programmable terminal called the Datapoint 2200 is the earliest known device that bears any significant resemblance to the modern personal computer.^[15] It was made by CTC (now known as Datapoint) in 1970 and was a complete system in a small case bearing the approximate footprint of an IBM Selectric typewriter. The system's CPU was constructed from a variety of discrete components, although the company had commissioned Intel to develop a single-chip processing unit; there was a falling out between CTC and Intel, and the chip Intel had developed wasn't used. Intel soon released a modified version of that chip as the Intel 8008, the world's first 8-bit microprocessor^[16]. The needs and requirements of the Datapoint 2200 therefore determined the nature of the 8008, upon which all successive processors used in IBM-compatible PCs were based. Additionally, the design of the Datapoint 2200's multi-chip CPU and the final design of the Intel 8008 were so similar that the two are largely software-compatible; therefore, the Datapoint 2200, from a practical perspective, can be regarded as if it were indeed powered by an 8008, which makes it a strong candidate for the title of "first microcomputer" as well

[edit] Altair 8800 and IMSAI 8080

Main articles: Altair 8800 and IMSAI 8080

Development of the single-chip microprocessor was an enormous catalyst to the popularization of cheap, easy to use, and truly personal computers. The Altair 8800, introduced in a Popular Electronics magazine article in the January 1975 issue, at the time set a new low price point for a computer, bringing computer ownership to an admittedly select market in the 1970s. This was followed by the IMSAI 8080 computer, with similar abilities and limitations. The Altair and IMSAI were essentially scaled-down minicomputers and were incomplete: to connect a keyboard or screen to them required heavy, expensive "peripherals". These machines both featured a front panel with switches and lights, which communicated with the operator in binary. To program the machine, one didn't simply power up: one first had to key in the bootstrap loader program in binary, then read in a paper tape containing a BASIC interpreter, using a massive paper-tape reader. Keying the loader required setting a bank of eight switches up or down and pressing the "load" button, once for each byte of the program, which was typically hundreds of bytes long. This was before one could begin to do any computing. (At the first West Coast Computer Faire, a three-year-old girl amused herself by flipping random switches and pressing the Load button, which were at her eye level, then moving on to the next demo. By doing so, she had inserted a random number into the location whose address was in the Program Counter, thus crashing the machine. She was followed by gasps and screams as the vendors discovered that they had to repeat the whole start-up cycle—her parents found her by heading for the commotion. The next Computer Faire banned small children. A Few years later, personal computers lost the switches and lights; thirty years later, they have memory protection, so that crashing a single program doesn't crash the machine.)^{[citation needed]}

In 1976, the Kooro Manufacturing & Electronics Cooperative in Skopje, Macedonia produced in limited quantities, an all in one (integrated keyboard, monochrome monitor, 8 inch floppy disk drive and 16k of ram) for use by government officials. Similar in appearance to the TRS-80 Model III computer using a proprietary operating system.^[17]

It was arguably the Altair computer that spawned the development of Apple, as well as Microsoft which produced and sold the Altair BASIC programming language interpreter, Microsoft's first product. The second generation of microcomputers — those that appeared in the late 1970s, sparked by the unexpected demand for the kit computers at the electronic hobbyist clubs, were usually known as home computers. For business use these systems were less capable and in some ways less versatile than the large business computers of the day. They were designed for fun and educational purposes, not so much for practical use. And although you could use some simple office/productivity applications on them, they were generally used by computer enthusiasts for learning to program and for running computer games, for which the personal computers of the period were less suitable and much too expensive. For the more technical hobbyists home computers were also used for electronics interfacing, such as controlling model railroads, and other general hobbyist pursuits.

[edit] Heathkit and Zenith

In 1978, the Heath company introduced the Heathkit H-8 computer. The early computers like the Altair had been sold as kits, but Heath had real experience in producing kit electronic equipment and the Heath name carried confidence with it. The H-8 was successful, as were the H-19 and H-29 terminals, and the H-89 one piece terminal/computer (The H-8 and H-89 ran their custom operating system, HDOS). The H-11, a low-end DEC PDP-11 16-bit computer, was less successful probably because it was substantially more expensive than the 8-bit computer line. (A generation earlier (1956),Heathkit sold a kit for a vacuum tube analog computer which could also be considered a form of personal computer^[18].

Zenith Radio Company bought Heath Company from Schlumberger in 1979, renaming the computer division Zenith Data Systems (ZDS). Zenith was in the vanguard of companies to start selling personal computers to small businesses. The H-89 kit was re-branded as the Z89/Z90, an assembled all in one system with a monitor and a floppy disk drive. They had agreements with Peachtree software to sell a customized "turn-key" version of their accounting, CPA and real estate management software. Shortly after the release of the Z90, they released a 5 MB hard disk unit and double density external floppy disk drives. While the H11 was popular with hard-core hobbyists, Heath engineers realized that DEC design would not be able to get Heath up the road to more powerful systems. Heath/Zenith then designed a dual Intel 8085/8088 based system dubbed the H-100 (or Z-100, in preassembled form). The machine featured very advanced (for the day) bit mapped video that allowed up to 640 x 512 pixels of 8 color graphics. The 100 was interesting in that it could run either the CP/M operating system, or their OEM version of MS-DOS (Z-DOS).

[edit] Apple II, TRS-80 and Commodore PET

Main articles: Apple II, TRS-80, and Commodore PET

The MOS Technology 6502 series microprocessor lead to a reduction in the expense of creating computing systems. The Commodore PET, the TRS 80, and the Apple II, also known as the 1977 Trinity by Byte magazine, are often cited as the first personal computers. Specifically, the Commodore PET, which Byte called the first ^[19]. The design of the Commodore PET, a single integrated machine with a built in monitor, keyboard, and datasette device, and a character set that made graphics easy to produce, went on to inspire the popular Macintosh computer, by Apple.

A 1978 ad for the Apple II used the wording "Apple, the personal computer". There was no trademark symbol. Three years later, the term "personal computer" was a trademark of IBM, which had decided to invade the microcomputer market and had done it successfully; a few years later, a judge declared that "personal computer" was no longer an IBM trademark.

[edit] Into homes

With the start of 1980s and the introduction of cheap personal computers home usage began to take off. Though initial models such as Sinclairs ZX80 were unimpressive and hence sold only in relatively small numbers it was with the introduction of home computers capable of playing more complex games, in colour with sound, such as the Atari and Sinclair Spectrum that opened millions of front doors to home computing.

[edit] Back to business

It was the launch of the VisiCalc spreadsheet, initially for the Apple II (and later for the Atari 8-bit family, Commodore PET, and IBM PC) that turned the microcomputer into a business tool. In fact, An Apple employee discovered in 1980 that IBM's San Jose research lab had purchased several Apple IIs, solely to run VisiCalc.^{[citation needed]}

This was followed by the August 12 1981 release of the IBM PC, which would revolutionize the computer market. The Lotus 1-2-3, a combined spreadsheet (inspired by VisiCalc), presentation graphics, and simple database application, would become the PC's own killer application. Good word processor programs didn't appear for personal computers until 1985. The earlier versions were dominated by WordStar but were not comparable to standalone word processors or those found on mini-computers. WordPerfect 4.1 for the IBM 5150 and Microsoft Word 1.0 for the Apple Macintosh both released in 1985 were enough reason to justify the entire cost of purchasing the computers for individual office workers giving these programs the status of killer applications.^[20]

On the January 3 1983 issue of Time magazine, the personal computer was named the "Person of the Year" for 1982.

[edit] Uses

Personal computers are normally operated by one user at a time to perform such general purpose tasks as word processing, Internet browsing, Internet faxing, e-mail and other digital messaging, multimedia playback, computer game play, computer programming, etc. The user of a modern personal computer may have significant knowledge of the operating environment and application programs, but is not necessarily interested in programming nor even able to write programs for the computer. Therefore, most software written primarily for personal computers tends to be designed with simplicity of use, or "user-friendliness" in mind. However, the software industry continuously provide a wide range of new products for use in personal computers, targeted at both the expert and the non-expert user.

[edit] Configuration

This section describes the typical personal computer called a desktop computer because one can easily look inside the case. The other types of personal computers have the same basic setup, but usually lack the peripherals.

[edit] Computer components

Main article: Computer hardware

A minimal setup of a typical contemporary desktop computer would be

• Computer case with power supply (usually sold together)
• Motherboard
• Processor with a heat sink and fan (usually sold together)
• At least one memory card
• Mass storage
• Keyboard and mouse for input
• Monitor for output

The motherboard connects everything together. The memory card(s), graphics card and processor, are mounted directly onto the motherboard (the processor in a socket and the memory and graphics cards in expansion slots). The mass storage is connected to it with cables and can be installed in the computer case or in a separate case. Same for keyboard and mouse, except that they are external and connect to the I/O panel on the back of the computer. The monitor is also connected to the I/O panel, either through an onboard port on the motherboard, or a port on the graphics card.

The mass storage can be

• Hard disk
• Floppy drive or Zip drive (both with removable media)
• Optical drive (CD or DVD, removable, usually read-only)
• Flash Storage (interal or memory card)

The operating system (e.g.: Microsoft Windows, Mac OS, Linux or many others) can be located on either of these, but typically it's on one of the hard disks. A LiveCD is also possible, but it is very slow and is usually used for installation of the OS, demonstrations, or problem solving.

On top of these, a computer may also have

• Sound card
• Video card
• Network card
• internal modem card (although less frequently these days).

Common additions, connected on the outside (peripherals), are

• Printer
• Scanner
• Webcam
• Speakers
• Microphone
• Modem
• router
• Headset
• Card reader
• Gaming devices such as a joystick

Several functions (implemented by chipsets) can be integrated into the motherboard, such as typically USB and network, but also graphics and sound. But even if these are present, a separate card can be added if what is available isn't sufficient.

The graphics and sound card can have a break out box to keep the analog parts away from the electromagnetic radiation inside the computer case. For really large amounts of data, a tape drive can be used or (extra) hard disks can be put together in an external case.

These components can usually be put together with little knowledge, to build a computer. If something shouldn't go somewhere, it usually doesn't fit (this used to not always be the case in the past) and if it does fit it can usually do little harm.

Most personal computers are standardized to the point that purchased software is expected to run with little or no customization for the particular computer. Many PCs are also user-upgradeable, especially desktop and workstation class computers. Devices such as main memory, mass storage, even the motherboard and central processing unit may be easily replaced by an end user. This upgradeability is, however, not indefinite due to rapid changes in the personal computer industry. A PC that was considered top-of-the-line five or six years prior may be impractical to upgrade due to changes in industry standards. Such a computer usually must be totally replaced once it's no longer suitable for its purpose. This upgrade and replacement cycle is partially related to new releases of the primary mass-market operating system, which tends to drive the acquisition of new hardware and tends to obsolete previously serviceable hardware (see planned obsolescence).

The hardware capabilities of personal computers can sometimes be extended by the addition of expansion cards connected via an expansion bus. Some standard peripheral buses often used for adding expansion cards in personal computers as of 2005 are PCI, AGP (a high-speed PCI bus dedicated to graphics adapters), and PCI Express. Most personal computers as of 2005 have multiple physical PCI expansion slots. Many also include an AGP bus and expansion slot or a PCI Express bus and one or more expansion slots, but few PCs contain both buses.

[edit] Motherboard

Main article: Motherboard

The motherboard (or mainboard) is the primary circuit board within a personal computer. Many other components connect directly or indirectly to the motherboard. Motherboards usually contain one or more CPUs, supporting circuitry -- usually integrated circuits (ICs) providing the interface between the CPU memory and input/output peripheral circuits, main memory, and facilities for initial setup of the computer immediately after being powered on (often called boot firmware or, in IBM PC compatible computers, a BIOS). In many portable and embedded personal computers, the motherboard houses nearly all of the PC's core components. Often a motherboard will also contain one or more peripheral buses and physical connectors for expansion purposes. Sometimes a secondary daughter board is connected with the motherboard to provide further expandability or to satisfy space constraints..

[edit] Central processing unit

Main article: Central processing unit

The central processing unit, or CPU, is that part of a computer which executes software program instructions. In older computers this circuitry was formerly on several printed circuit boards, but in PC class machines, has been from the first personal computers, a single integrated circuit. Nearly all PCs contain a type of CPU known as a microprocessor. The microprocessor often plugs into the motherboard using one of many different types of socket. IBM PC compatible computers use an x86-compatible processor, usually made by Intel, AMD, VIA Technologies or Transmeta. Apple Macintosh computers were initially built with the Motorola 680x0 family of processors, then switched to the PowerPC series (a RISC architecture jointly developed by Apple Computer, IBM and Motorola), but as of 2006, Apple has switched again, this time to x86 compatible processors.

[edit] Main memory

Main article: Primary storage

A PC's main memory (i.e., its 'primary store') is fast storage that is directly accessible by the CPU, and is used to store the currently executing program and immediately needed data. PCs use semiconductor random access memory (RAM) of various kinds such as DRAM or SRAM as their primary storage. Which exact kind depends on cost/performance issues at any particular time. Main memory is much faster than mass storage devices like hard disks or optical discs, but is usually volatile, meaning it does not retain its contents (instructions or data) in the absence of power, and is much more expensive for a given capacity than is most mass storage. Main memory is generally not suitable for long-term or archival data storage.

[edit] Mass storage

Main article: Hard disk

Mass storage devices store programs and data even when the power is off; they do require power to perform read/write functions during usage. Although semiconductor flash memory has dropped in cost, the prevailing form of mass storage in personal computers is still the electromechanical hard disk.

The disk drives use a sealed head/disk assembly (HDA) which was first introduced by IBM's "Winchester" disk system. The use of a sealed assembly allowed the use of positive air pressure to drive out particles from the surface of the disk, which improves reliability.

If the mass storage controller provides for expandability, a PC may also be upgraded by the addition of extra hard disk or optical disc drives. For example, DVD-ROMs, CD-ROMs, and various optical disc recorders may all be added by the user to certain PCs. Standard internal storage device interfaces are ATA, Serial ATA, SCSI, and CF+ Type II in 2005.

[edit] Video card

Main article: Video card

The video card - otherwise called a graphics card, graphics adapter or video adapter - processes and renders the graphics output from the computer to the computer display, also called the visual display unit (VDU), and is an essential part of the modern computer. On older models, and today on budget models, graphics circuitry tended to be integrated with the motherboard but, for modern flexible machines, they are supplied in PCI, AGP, or PCI Express format.

When the IBM PC was introduced, many existing personal computers used text-only display adapters and had no graphics capability.

[edit] Laptop computers

Main article: Laptop

A laptop computer or simply laptop, also called a notebook computer or sometimes a notebook, is a small personal computer designed for mobility. 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. Most laptops contain batteries to facilitate operation without a readily available electrical 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.

[edit] Potential health risks

Health risks include neck and spine issues, and eye strain which can potentially result in headaches and back pain due to incorrect posture and focus on one task, as well as repetitive stress injury caused by repeated typing and clicking, and obesity issues caused by lack of exercise.^[21]

[edit] See also

• List of early non-IBM-PC-compatible PCs
• Desktop replacement computer
• Desktop computer
• IBM Corporation
• Microsoft Corporation
• Apple, Inc.
• Gaming PC
• Mainframe computer
• Microcomputer
• Minicomputer
• Personal Computer Museum
• Silent PC
• Supercomputer
• Workstation
• Public computer
• List of computer system manufacturers

[edit] Notes

[edit] Further reading

• Accidental Empires: How the boys of Silicon Valley make their millions, battle foreign competition, and still can't get a date, Robert X. Cringely, Addison-Wesley Publishing, (1992), ISBN 0-201-57032-7

[edit] External links

• Personal Computer Museum – Showcasing over 40 interactive displays
• Old Computers Museum – Displaying over 100 historic machines.
• Chronology of Personal Computers A chronology of computers from 1947 on.
• Notebook PC Reviews
• Howstuffworks' article on "How PCs Work"
• BlinkenLights Archaeological Insititute - Personal Computer Milestones What was the first personal computer?
• "Total share: 30 years of personal computer market share figures" – From Ars Technica

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