Personal computer

File:Altair8800.jpg

The Altair 8800 was among the first microcomputers to be affordable by an individual, although it initially lacked peripherals and memory.

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

We may never know 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". This advertisement was too extreme for the target audience and replaced with a much drier ad for the HP 9100A programmable calculator. 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" 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." Two years later when the 1977 Trinity of preassembled small computers hit the markets, the Apple II and the PET 2001 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 home computers were sold and the youth of the day had a new concept of the personal computer.

Personal computers are also known as microcomputers and home computers. Often, the term "personal computer" is used exclusively for computers running a Microsoft Windows operating system, but this is erroneous. For example, a Macintosh running Mac OS and an IBM PC compatible running Linux are both personal computers. This confusion stems from the fact that the term "PC" is often used as a shorthand form for "IBM PC compatible" and historically Mac OS has run on non-IBM compatible hardware like the PowerPC architecture. Linux runs on virtually any kind of hardware, but was developed later and has not achieved popularity comparable to Microsoft Windows.

History

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

Mainframes and large minicomputers

Time shared computer terminals connected to central computers, such as the TeleVideo ASCII character mode smart terminal pictured here, were sometimes used before the advent of the PC. But is however recognized as a "dumb terminal" to today's standards.

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. The minicomputer era was an intermediary step from mainframes to personal computer usage.

Minicomputers were available to smaller organizations than those that once used mainframes, but were not aimed at individuals, Ken Olsen, founder of DEC, has been widely quoted as saying in 1971 "I can think of no reason why an individual would want to own a computer." This was understandable, considering what DEC was offering: only a fairly large organization could use or afford a machine the size of an average home refrigerator that required external terminals to operate and program. A few individuals, such as Steve Wozniak, had differing views, as will be seen below.

Computers at home

The 1977 Apple II, one of the 1977 Trinity Floppy drive pictured was 3rd party addition.

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."

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. Olsen did not ask them, because minicomputers were still selling.

A programmable terminal called the Datapoint 2200 is the earliest known device that bears any significant resemblance to the modern personal computer. 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. 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.

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 8800 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.

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.

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 and the Steve Wozniak-designed Apple release, the Apple I — 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.

The MOS 6500 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 . The design of the Commodore PET, a single integrated machine with a built in monitor, keyboard, and datasette device, and the operating system of the Xerox Alto 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 Apple's turf and had done it successfully; a few years later, a judge declared that "personal computer" was no longer an IBM trademark, but a generic term for any personal computer not made by Apple.

Back to business

File:IBM PC 5150 Image.jpg

A release photo of the original IBM PC (ca. 1981).

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.

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 would also appear for many home computers, in particular the introduction of Microsoft Word for the Apple Macintosh in 1985 (while earlier versions of Word had been created for the PC, it became popular initially through the Macintosh).

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

Today

A university computer lab containing many desktop PCs

During the 1990s, the power of personal computers increased radically, blurring the formerly sharp distinction between personal computers and multi-user computers, such as mainframes. Today higher-end computers often distinguish themselves from personal computers by greater reliability or greater ability to multitask, rather than by brute CPU ability alone.

In today's common usage, personal computer and PC usually indicate an IBM PC compatible. Due to this association, some manufacturers of personal computers that are not IBM PCs avoid explicitly using the terms to describe their products.

Due to networks, the Internet and such factors as digital rights management, modern personal computers are no longer the exclusive tools of their users. Support of desktop computers in business now requires as much bureaucracy and professional training as did operating a time-sharing system, with the drawback of much lower security and many users skilled enough to get into trouble but not skilled enough to get out.

Modern computers are thousands of times more powerful than those of only twenty years ago. Multi-core processors, a gigabyte of RAM and hard drives of several hundred gigabytes have become the norm. These numbers eclipse even supercomputers from past decades.

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.

Configuration

An exploded view of a modern personal computer:

1. Monitor
2. Motherboard
3. CPU (Microprocessor)
4. Primary storage (RAM)
5. Expansion cards
6. Power supply
7. Optical disc drive
8. Secondary storage (Hard disk)
9. Keyboard
10. Mouse

Personal computers can be categorized by size and portability:

• Desktop computers
• Laptop or notebooks
• Personal digital assistants (PDAs)
• Portable computers
• Tablet computers
• Wearable computers

This section describes the desktop computer because it's the most complete and one can easily look inside the case. The others have the same basic setup, but usually lack the peripherals.

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 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 an expansion slot). The mass storage is connected to it with cables. Same for keyboard and mouse, except that they are external and connect to the back plate. The monitor is also connected to the back plate, except not (usually) directly to the motherboard, but to a connector in the graphics card.

The mass storage can be:

• Hard disk
• Floppy drive or zip drive (both with media)
• Optical drive (CD or DVD)

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

On top of these, a typical computer also has:

• Sound card
• Network card
• Modem and possibly router

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

• Printer
• Scanner
• Webcam
• Speakers
• Microphone
• 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.

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.

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 Power PC series (a RISC architecture jointly developed by IBM, Motorola, and Apple Computer), but as of 2006, Apple has switched again, this time to x86 compatible processors.

Main memory

Main article: Primary storage

A four-megabyte RAM card measuring about twenty-two by fifteen inches (56 by 38 centimeters); made for the VAX 8600 minicomputer (ca. 1986). Dual in-line package (DIP)  Integrated circuits populate nearly the whole board; the RAM chips are the most common kind, and located in the rectangular areas to the left and right.

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.

Mass storage

Main article: Hard disk

Internals of a Winchester hard drive with the disks removed.

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 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.

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.

Laptop computers

Main article: Laptop

A laptop computer or simply laptop, also called a notebook computer or 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.

List of other non-IBM-PC-compatible business PCs

Pre-IBM-PC personal business computer systems

This is a list of non IBM PC compatible business personal computers (PC), and Personal Workstation (PW) computers, that came on the market before the IBM-PC (August 1981).

• Apple III designed as a business system by Apple Inc.
• Astrocom 760 by Astrocom Corporation
• C4P and C8P systems made by Ohio Scientific
• Commodore Business Machines (CBM) a series of mostly compatible machines by Commodore International
• CompuColor 8001 by Intecolor
• Cromemco (S-100 compatible computers)
• DEC Professional (computer) from Digital Equipment Corporation - three models
• The Digital Group (multiple platform microcomputers)
• DPS-1 by Intersystems
• Gimix (SS-50 SWTPC compatible computers)
• Helix (SS-50 (and later SS-64) SWTPC compatible computers)
• Midwest Scientific (SS-50 SWTPC compatible computers)
• Morrow Designs (S-100 compatible computers)
• NorthStar Horizon by North Star Computers
• HP-85A From Hewlett-Packard
• MSI computer systems from Midwest Scientific Instruments
• M20 from Olivetti
• Noval 760 by Noval/Gremlin
• Ohio Scientific (multiple platfomrs micro computers)
• QDP-100 and QDP-8100 systems from Quasar Computer Systems
• RCC REX by Realistic Controls Corporation
• S-100 bus systems, built from components made by various companies, mostly running CP/M
• SBC/9 by Percom
• SBS-8000 by Small Business systems
• Sol-20 by Processor Technology
• Sphere computer by Sphere inc.
• Smoke Signal Broadcasting (SS-50 SWTPC compatible computers)
• Superbrain by intertec Data Systems
• Telmac 1800 by the Finnish company Telercas
• SWTPC (South West Technical Products Corporation) systems
• Tano Systems (SS-50 SWTPC compatible computers)
• TRS-80 model I and Model II by Tandy Corporation
• H-8 CP/M microcomputer by Heathkit
• Z-89 by Zenith/Heathkit

Post-IBM-PC personal business computer systems

This is a list of non IBM PC compatible business personal computers (PC), and Personal Workstation (PW) computers, that came on the market after the IBM-PC (August 1981).

• Acorn Archimedes & RiscPC
• ACT Apricot by ACT (runs MS-DOS but is not IBM PC compatible.)
• Apple Lisa by Apple Inc.
• Amiga (previously produced by Commodore, now under license from Amiga Inc.)
• Amstrad PCW series (Personal Computer Word processor) from Amstrad
• Atari ST
• BeOS BeBox
• C-10 by Cromemco
• Commodore 64 by Commodore
• Compustar II VPU Model 20 by Intertec
• Corvus Concept by Corvus Systems
• HP 150 by Hewlett-Packard (Runs MS-DOS but is NOT IBM PC compatible.)
• Kaypro 10 by Kaypro
• Knowledge Worker by A.B.Dick Comp.
• Micro 16s by Fujitsu
• Micro Decision by Morrow Designs
• MTU-130 by Micro Technology Unlimited
• NeXT workstations by Next Software
• The NorthStar Advantage by Northstar (could run MS-DOS with an optional 8086 CPU plugin card).
• PC-8800 system from NEC (8-bit Z80 system running CP/M)
• PC-9800 system from NEC (Runs MS-DOS but is NOT IBM PC compatible.)
• Pegasos by Genesi
• QX-10 by Epson
• Rainbow 100 from Digital Equipment Corporation (Runs MS-DOS but is NOT IBM PC compatible.)
• RoadRunner from MicroOffice
• Series 999 by Golden West Computers
• SGI workstations like the SGI Indigo and SGI Onyx
• Sun SPARCstation
• TRS-80 model 16, 16e and 6000 by Tandy Corporation
• TI Professional Computer by Texas Instruments
• Tulip System-1 by Tulip Computers company (Runs MS-DOS but is NOT IBM PC compatible.)
• Victor 9000 by Sirius Systems Technology (Runs MS-DOS but is NOT IBM PC compatible.)

See also

• Linux
• Microsoft Windows
• Computer
• CP/M
• Desktop replacement computer
• Gaming PC
• History of computing hardware (1960s-present)
• Home computer
• HTPC
• Laptop
• Mainframe computer
• Microcomputer
• Minicomputer
• Osborne 1
• Apple Inc., Apple II, Apple Lisa, and Macintosh
• TRS-80, Commodore PET
• Personal Computer Museum
• Silent PC
• Supercomputer
• Workstation
• Xerox Star
• Public computer
• List of computer system manufacturers

Further reading

• John Markoff: What the Dormouse Said (ISBN 978-0143036760), Viking 2005. How the sixties counterculture shaped the personal computer industry.

External links

• Personal Computer Museum – Showcasing over 40 interactive displays
• Rune's PC Museum
• Howstuffworks' article on "How PCs Work"
• Wikicity for PC enthuiasm
• All about personal computers for kids
• 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