The IBM Personal Computer (model 5150, commonly known as the IBM PC) is the first
microcomputer
A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (PC ...
released in the IBM PC model line and the basis for the
IBM PC compatible
IBM PC compatible computers are similar to the original IBM PC, XT, and AT, all from computer giant IBM, that are able to use the same software and expansion cards. Such computers were referred to as PC clones, IBM clones or IBM PC clones. ...
de facto standard
A ''de facto'' standard is a custom or convention that has achieved a dominant position by public acceptance or market forces (for example, by early entrance to the market). is a Latin phrase (literally " in fact"), here meaning "in practice b ...
. Released on August 12, 1981, it was created by a team of engineers and designers directed by
Don Estridge
Philip Donald Estridge (June 23, 1937 – August 2, 1985), known as Don Estridge, was an American computer engineer who led development of the original IBM Personal Computer (PC), and thus is known as the "father of the IBM PC". His decisions dra ...
in
Boca Raton, Florida
Boca Raton ( ; es, Boca Ratón, link=no, ) is a city in Palm Beach County, Florida, United States. It was first incorporated on August 2, 1924, as "Bocaratone," and then incorporated as "Boca Raton" in 1925. The population was 97,422 in the ...
.
The machine was based on
open architecture
Open architecture is a type of computer architecture or software architecture intended to make adding, upgrading, and swapping components with other computers easy. For example, the IBM PC, Amiga 500 and Apple IIe have an open architecture support ...
and third-party peripherals. Over time, expansion cards and software technology increased to support it.
The PC had a
substantial influence on the personal computer market. The specifications of the IBM PC became one of the most popular computer design standards in the world. The only significant competition it faced from a non-compatible platform throughout the 1980s was from the Apple
Macintosh
The Mac (known as Macintosh until 1999) is a family of personal computers designed and marketed by Apple Inc., Apple Inc. Macs are known for their ease of use and minimalist designs, and are popular among students, creative professionals, and ...
product line. The majority of modern personal computers are distant descendants of the IBM PC.
History
Prior to the 1980s, IBM had largely been known as a provider of business computer systems.
As the 1980s opened, their market share in the growing minicomputer market failed to keep up with competitors, while other manufacturers were beginning to see impressive profits in the microcomputer space. The market for personal computers was dominated at the time by Tandy, Commodore and Apple, whose machines sold for several hundred dollars each and had become very popular. The microcomputer market was large enough for IBM's attention, with $15 billion in sales by 1979 and projected annual growth of more than 40% during the early 1980s. Other large technology companies had entered it, such as
Hewlett-Packard
The Hewlett-Packard Company, commonly shortened to Hewlett-Packard ( ) or HP, was an American multinational information technology company headquartered in Palo Alto, California. HP developed and provided a wide variety of hardware components ...
,
Texas Instruments
Texas Instruments Incorporated (TI) is an American technology company headquartered in Dallas, Texas, that designs and manufactures semiconductors and various integrated circuits, which it sells to electronics designers and manufacturers globall ...
and
Data General
Data General Corporation was one of the first minicomputer firms of the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation (DEC).
Their first product, 1969's Data General Nova, was a 16-bit minicomputer ...
, and some large IBM customers were buying Apples.
As early as 1980 there were rumors of IBM developing a personal computer, possibly a miniaturized version of the
IBM System/370
The IBM System/370 (S/370) is a model range of IBM mainframe computers announced on June 30, 1970, as the successors to the System/360 family. The series mostly maintains backward compatibility with the S/360, allowing an easy migration path f ...
,
and
Matsushita acknowledged publicly that it had discussed with IBM the possibility of manufacturing a personal computer in partnership, although this project was abandoned.
The public responded to these rumors with skepticism, owing to IBM's tendency towards slow-moving, bureaucratic business practices tailored towards the production of large, sophisticated and expensive business systems.
As with other large computer companies, its new products typically required about four to five years for development,
and a well publicized quote from an industry analyst was, "IBM bringing out a personal computer would be like teaching an elephant to tap dance."
IBM had previously produced microcomputers, such as 1975's
IBM 5100
The IBM 5100 Portable Computer is a portable computer (one of the first) introduced in September 1975, six years before the IBM Personal Computer, and eight before the first successful IBM compatible portable computer, the Compaq Portable. It ...
, but targeted them towards businesses; the 5100 had a price tag as high as $20,000. Their entry into the home computer market needed to be competitively priced.
In 1980, IBM president John Opel, recognizing the value of entering this growing market, assigned
William C. Lowe to the new Entry Level Systems unit in Boca Raton, Florida. Market research found that computer dealers were very interested in selling an IBM product, but they insisted the company use a design based on standard parts, not IBM-designed ones so that stores could perform their own repairs rather than requiring customers to send machines back to IBM for service.
Atari proposed to IBM in 1980 that it act as original equipment manufacturer for an IBM microcomputer,
a potential solution to IBM's known inability to move quickly to meet a rapidly changing market. The idea of acquiring Atari was considered but rejected in favor of a proposal by Lowe that by forming an independent internal working group and abandoning all traditional IBM methods, a design could be delivered within a year and a prototype within 30 days. The prototype worked poorly but was presented with a detailed business plan which proposed that the new computer have an
open architecture
Open architecture is a type of computer architecture or software architecture intended to make adding, upgrading, and swapping components with other computers easy. For example, the IBM PC, Amiga 500 and Apple IIe have an open architecture support ...
, use non-proprietary components and software, and be sold through retail stores, all contrary to IBM practice. It also estimated sales of 220,000 computers over three years, more than IBM's entire
installed base
Installed base (also install base, install ''ed'' user base or just user base) is a measure of the number of units of a product or service that are actually in use, as opposed to market share, which only reflects sales over a particular period. ...
.
[Atkinson, P, (2013) ''DELETE: A Design History of Computer Vapourware]
London: Bloomsbury Publishing.
This swayed the Corporate Management Committee, which converted the group into a business unit named "Project Chess", and provided the necessary funding and authority to do whatever was needed to develop the computer in the given timeframe. The team received permission to expand to 150 people by the end of 1980, and in one day more than 500 IBM employees called in asking to join.
Design process
The design process was kept under a policy of strict secrecy, with all other IBM divisions kept in the dark about the project.
Several CPUs were considered, including the
Texas Instruments TMS9900
Introduced in June 1976, the TMS9900 was one of the first commercially available, single-chip 16-bit microprocessors. It implemented Texas Instruments' TI-990 minicomputer architecture in a single-chip format, and was initially used for low-end ...
,
Motorola 68000
The Motorola 68000 (sometimes shortened to Motorola 68k or m68k and usually pronounced "sixty-eight-thousand") is a 16/32-bit complex instruction set computer (CISC) microprocessor, introduced in 1979 by Motorola Semiconductor Products Sector ...
and
Intel 8088
The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers an ...
. The 68000 was considered the best choice,
but was not production-ready like the others.
The
IBM 801
The 801 was an experimental central processing unit (CPU) design developed by IBM during the 1970s. It is considered to be the first modern RISC design, relying on processor registers for all computations and eliminating the many variant address ...
RISC processor was also considered, since it was considerably more powerful than the other options, but rejected due to the design constraint to use off-the-shelf parts.
IBM chose the 8088 over the similar but superior
8086
The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...
because Intel offered a better price for the former and could provide more units,
and the 8088's 8-bit bus reduced the cost of the rest of the computer. The 8088 had the advantage that IBM already had familiarity with the 8085 from designing the
IBM System/23 Datamaster
The System/23 Datamaster (Model 5322 desktop model and Model 5324 floor model) was announced by IBM in July 1981. The Datamaster was the least expensive IBM computer until the far less expensive and far more popular IBM PC was announced in the fo ...
. The 62-pin expansion bus slots were also designed to be similar to the Datamaster slots, and its keyboard design and layout became the
Model F keyboard shipped with the PC,
but otherwise the PC design differed in many ways.
The 8088 motherboard was designed in 40 days, with a working prototype created in four months, demonstrated in January 1981. The design was essentially complete by April 1981, when it was handed off to the manufacturing team. PCs were assembled in an IBM plant in Boca Raton, with components made at various IBM and third party factories. The monitor was an existing design from
IBM Japan
IBM has had business internationally since before the company had a name. Early leaders of the companies that would eventually become IBM (Mr Hollerith, Mr Flint, and Mr Watson) all were involved in doing international business.
In those early day ...
; the printer was manufactured by
Epson
Seiko Epson Corporation, or simply known as Epson, is a Japanese multinational electronics company and one of the world's largest manufacturers of computer printers and information- and imaging-related equipment. Headquartered in Suwa, Nagano, ...
. Because none of the functional components were designed by IBM, they obtained no patents on the PC.
Many of the designers were computer hobbyists who owned their own computers, including many Apple II owners, which influenced the decisions to design the computer with an
open architecture
Open architecture is a type of computer architecture or software architecture intended to make adding, upgrading, and swapping components with other computers easy. For example, the IBM PC, Amiga 500 and Apple IIe have an open architecture support ...
and publish technical information so others could create compatible software and
expansion slot
Expansion may refer to:
Arts, entertainment and media
* ''L'Expansion'', a French monthly business magazine
* ''Expansion'' (album), by American jazz pianist Dave Burrell, released in 2004
* ''Expansions'' (McCoy Tyner album), 1970
* ''Expansio ...
peripherals.
During the design process IBM avoided vertical integration as much as possible, for example choosing to license
Microsoft BASIC
Microsoft BASIC is the foundation software product of the Microsoft company and evolved into a line of BASIC interpreters and compiler(s) adapted for many different microcomputers. It first appeared in 1975 as Altair BASIC, which was the first ve ...
rather than utilizing the in-house version of BASIC used for mainframes due to the better existing public familiarity with the Microsoft version.
Debut
The IBM PC debuted on August 12, 1981 after a twelve-month development. Pricing started at $1,565 for a configuration with 16 KB RAM,
Color Graphics Adapter
The Color Graphics Adapter (CGA), originally also called the ''Color/Graphics Adapter'' or ''IBM Color/Graphics Monitor Adapter'', introduced in 1981, was IBM's first color graphics card for the IBM PC and established a de facto computer display ...
, and no disk drives. The price was designed to compete with comparable machines in the market.
For comparison, the Datamaster, announced two weeks earlier as IBM's least expensive computer, cost $10,000.
IBM's marketing campaign licensed the likeness of
Charlie Chaplin
Sir Charles Spencer Chaplin Jr. (16 April 188925 December 1977) was an English comic actor, filmmaker, and composer who rose to fame in the era of silent film. He became a worldwide icon through his screen persona, the Tramp, and is consider ...
's character "The Little Tramp" for a series of advertisements based on Chaplin's movies, played by Billy Scudder.
The PC was IBM's first attempt to sell a computer through retail channels rather than directly to customers. Because IBM did not have retail experience, they partnered with the retail chains
ComputerLand
ComputerLand was a widespread chain of retail computer stores during the early years of the microcomputer revolution, and was one of the outlets (along with Computer City and Sears) chosen to introduce the IBM PC in 1981. The first ComputerLand op ...
and
Sears
Sears, Roebuck and Co. ( ), commonly known as Sears, is an American chain of department stores founded in 1892 by Richard Warren Sears and Alvah Curtis Roebuck and reincorporated in 1906 by Richard Sears and Julius Rosenwald, with what began a ...
, who provided important knowledge of the marketplace
and became the main outlets for the PC. More than 190 ComputerLand stores already existed, while Sears was in the process of creating a handful of in-store computer centers for sale of the new product.
Reception was overwhelmingly positive, with analysts estimating sales volume in the billions of dollars in the first few years after release.
After release, IBM's PC immediately became the talk of the entire computing industry.
Dealers were overwhelmed with orders, including customers offering pre-payment for machines with no guaranteed delivery date.
By the time the machine began shipping, the term "PC" was becoming a household name.
Success
Sales exceeded IBM's expectations by as much as 800%, with the company at one point shipping as many as 40,000 PCs per month.
IBM estimated that home users made up 50 to 70% of purchases from retail stores.
In 1983, IBM sold more than 750,000 machines, while
Digital Equipment Corporation
Digital Equipment Corporation (DEC ), using the trademark Digital, was a major American company in the computer industry from the 1960s to the 1990s. The company was co-founded by Ken Olsen and Harlan Anderson in 1957. Olsen was president unt ...
, one of the companies whose success had spurred IBM to enter the market, sold only 69,000.
Software support from the industry grew rapidly, with the IBM nearly instantly becoming the primary target for most microcomputer software development.
One publication counted 753 software packages available a year after the PC's release, four times as many as were available for the Macintosh a year after its launch.
Hardware support also grew rapidly, with 30–40 companies competing to sell memory expansion cards within a year.
By 1984, IBM's revenue from the PC market was $4 billion, more than twice that of Apple.
A 1983 study of corporate customers found that two thirds of large customers standardizing on one computer chose the PC, while only 9% chose Apple. A 1985 ''
Fortune
Fortune may refer to:
General
* Fortuna or Fortune, the Roman goddess of luck
* Luck
* Wealth
* Fortune, a prediction made in fortune-telling
* Fortune, in a fortune cookie
Arts and entertainment Film and television
* ''The Fortune'' (1931 film) ...
'' survey found that 56% of American companies with personal computers used PCs while 16% used Apple.
Almost as soon as the PC reached the market, rumors of clones began,
and the first PC compatible clone was released in June 1982, less than a year after the PC's debut.
Hardware
![8088-inside-1](https://upload.wikimedia.org/wikipedia/commons/8/84/8088-inside-1.jpg)
For low cost and a quick design turnaround time, the hardware design of the IBM PC used entirely "off-the-shelf" parts from third party manufacturers, rather than unique hardware designed by IBM.
The PC is housed in a wide, short steel chassis intended to support the weight of a CRT monitor. The front panel is made of plastic, with an opening where one or two disk drives can be installed. The back panel houses a power inlet and switch, a keyboard connector, a cassette connector and a series of tall vertical slots with blank metal panels which can be removed in order to install expansion cards.
Internally, the chassis is dominated by a motherboard which houses the CPU, built-in RAM, expansion RAM sockets, and slots for expansion cards.
The IBM PC was highly expandable and upgradeable, but the base factory configuration included:
Motherboard
The PC is built around a single large circuit board called a
motherboard
A motherboard (also called mainboard, main circuit board, mb, mboard, backplane board, base board, system board, logic board (only in Apple computers) or mobo) is the main printed circuit board (PCB) in general-purpose computers and other expand ...
which carries the processor, built-in RAM, expansion slots, keyboard and cassette ports, and the various peripheral integrated circuits that connected and controlled the components of the machine.
The peripheral chips included an
Intel 8259
The Intel 8259 is a Programmable Interrupt Controller (PIC) designed for the Intel 8085 and Intel 8086 microprocessors. The initial part was 8259, a later A suffix version was upward compatible and usable with the 8086 or 8088 processor. The 82 ...
PIC, an
Intel 8237
Intel 8237 is a direct memory access (DMA) controller, a part of the MCS 85 microprocessor family. It enables data transfer between memory and the I/O with reduced load on the system's main processor by providing the memory with control signals a ...
DMA controller, and an
Intel 8253
The Intel 8253 and 8254 are programmable interval timers (PITs), which perform timing and counting functions using three 16-bit counters.
The 825x family was primarily designed for the Intel 8080/ 8085-processors, but were later used in x86 ...
PIT. The PIT provides clock "ticks" and dynamic memory refresh timing.
CPU and RAM
![Ibm5150mobo1984black](https://upload.wikimedia.org/wikipedia/commons/7/7d/Ibm5150mobo1984black.jpg)
The CPU is an
Intel 8088
The Intel 8088 ("''eighty-eighty-eight''", also called iAPX 88) microprocessor is a variant of the Intel 8086. Introduced on June 1, 1979, the 8088 has an eight-bit external data bus instead of the 16-bit bus of the 8086. The 16-bit registers an ...
, a cost-reduced form of the
Intel 8086
The 8086 (also called iAPX 86) is a 16-bit microprocessor chip designed by Intel between early 1976 and June 8, 1978, when it was released. The Intel 8088, released July 1, 1979, is a slightly modified chip with an external 8-bit data bus (allowi ...
which largely retains the 8086's internal 16-bit logic, but exposes only an 8-bit bus.
The CPU is clocked at 4.77 MHz, which would eventually become an issue when clones and later PC models offered higher CPU speeds that broke compatibility with software developed for the original PC. The single base clock frequency for the system was 14.31818 MHz, which when divided by 3, yielded the 4.77 MHz for the CPU (which was considered close enough to the then 5 MHz limit of the 8088), and when divided by 4, yielded the required 3.579545 MHz for the NTSC color carrier frequency.
The PC motherboard included a second, empty socket, described by IBM simply as an "auxiliary processor socket", although the most obvious use was the addition of an
Intel 8087
The Intel 8087, announced in 1980, was the first x87 floating-point coprocessor for the 8086 line of microprocessors.
The purpose of the 8087 was to speed up computations for floating-point arithmetic, such as addition, subtraction, multiplicati ...
math coprocessor, which improved
floating-point math performance.
From the factory the PC was equipped with either 16 KB or 64 KB of RAM. RAM upgrades were provided both by IBM and third parties as expansion cards, and could upgrade the machine to a maximum of 256 KB on the motherboard, and 640 KB total.
ROM BIOS
The BIOS is the firmware of the IBM PC, occupying one 8 KB chip on the motherboard. It provides bootstrap code and a library of common functions that all software can use for many purposes, such as video output, keyboard input, disk access, interrupt handling, testing memory, and other functions. IBM shipped three versions of the BIOS throughout the PC's lifespan.
Display
![Ibm px xt color](https://upload.wikimedia.org/wikipedia/commons/6/6a/Ibm_px_xt_color.jpg)
While most home computers had built-in video output hardware, IBM took the unusual approach of offering two different graphics options, the
MDA
MDA, mda, or ''variation'', may refer to:
Places
* Moldova, a country in Europe with the ISO 3166-1 country code MDA Politics
* Meghalaya Democratic Alliance (2018), ruling coalition government in the Indian State of Meghalaya led by National Pe ...
and
CGA cards. The former provided high-resolution monochrome text, but could not display anything except text, while the latter provided medium- and low-resolution color graphics and text.
CGA used the same scan rate as NTSC television, allowing it to provide a composite video output which could be used with any compatible television or
composite monitor
A composite monitor or composite video monitor is any analog video display that receives input in the form of an analog composite video signal to a defined specification. A composite video signal encodes all information on a single conductor; a ...
, as well as a direct-drive TTL output suitable for use with any RGBI monitor using an NTSC scan rate. IBM also sold the 5153 color monitor for this purpose, but it was not available at release
and was not released until March 1983.
MDA scanned at a higher frequency and required a proprietary monitor, the
IBM 5151
The IBM 5151 is a 12" transistor–transistor logic (TTL) monochrome monitor, shipped with the original IBM Personal Computer for use with the IBM Monochrome Display Adapter. A few other cards were designed to work with it, such as the Hercules Gra ...
. The card also included a built-in printer port.
Both cards could also be installed simultaneously for mixed graphics and text applications. For instance,
AutoCAD
AutoCAD is a commercial computer-aided design (CAD) and drafting software application. Developed and marketed by Autodesk, AutoCAD was first released in December 1982 as a desktop app running on microcomputers with internal graphics controllers. ...
,
Lotus 1-2-3
Lotus 1-2-3 is a discontinued spreadsheet program from Lotus Software (later part of IBM). It was the first killer application of the IBM PC, was hugely popular in the 1980s, and significantly contributed to the success of IBM PC-compatibles i ...
and other software allowed use of a CGA Monitor for graphics and a separate
monochrome monitor
A monochrome monitor is a type of computer monitor in which computer text and images are displayed in varying tones of only one color, as opposed to a color monitor that can display text and images in multiple colors. They were very common in t ...
for text menus. Third parties went on to provide an enormous variety of aftermarket graphics adapters, such as the
Hercules Graphics Card The Hercules Graphics Card (HGC) is a computer graphics controller made by Hercules Computer Technology, Inc. that combines IBM's text-only MDA display standard with a bitmapped graphics mode. This allows the HGC to offer both high-quality text an ...
.
The software and hardware of the PC, at release, was designed around a single 8-bit adaptation of the ASCII character set, now known as
code page 437
Code page 437 (CCSID 437) is the character set of the original IBM PC (personal computer). It is also known as CP437, OEM-US, OEM 437, PC-8, or DOS Latin US. The set includes all printable ASCII characters as well as some accented letters (diacri ...
.
Storage
The two bays in the front of the machine could be populated with one or two 5.25″ floppy disk drives, storing 160 KB per disk side for a total of 320 KB of storage on one disk.
The floppy drives require a controller card inserted in an expansion slot, and connect with a single ribbon cable with two edge connectors. The IBM floppy controller card provides an external 37-pin D-sub connector for attachment of an external disk drive, although IBM did not offer one for purchase until 1986.
As was common for home computers of the era, the IBM PC offered a port for connecting a
cassette data recorder. Unlike the typical home computer however, this was never a major avenue for software distribution, probably because very few PCs were sold without floppy drives. The port was removed on the very next PC model, the XT.
At release, IBM did not offer any hard disk drive option
and adding one was difficult - the PC's stock power supply had inadequate power to run a hard drive, the motherboard did not support BIOS expansion ROMs which was needed to support a hard drive controller, and both PC DOS and the BIOS had no support for hard disks. After the XT was released, IBM altered the design of the 5150 to add most of these capabilities, except for the upgraded power supply. At this point adding a hard drive was possible, but required the purchase of the IBM 5161 Expansion Unit, which contained a dedicated power supply and included a hard drive.
Although official hard drive support did not exist, the third party market did provide early hard drives that connected to the floppy disk controller, but required a patched version of PC DOS to support the larger disk sizes.
Human interface
![IBM Model F XT](https://upload.wikimedia.org/wikipedia/commons/5/56/IBM_Model_F_XT.png)
The only option for
human interface
In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fr ...
provided in the base PC was the built-in keyboard port, meant to connect to the included
Model F keyboard. The Model F was initially developed for the
IBM Datamaster, and was substantially better than the keyboards provided with virtually all home computers on the market at that time in many regards - number of keys, reliability and ergonomics. While some home computers of the time utilized
chiclet keyboard
A chiclet keyboard or island-style keyboard is a computer keyboard with keys that form an array of small, flat rectangular or lozenge-shaped rubber or plastic keys that look like erasers or "Chiclets", a brand of chewing gum manufactured in the s ...
s or inexpensive mechanical designs, the IBM keyboard provided good ergonomics, reliable and positive tactile key mechanisms and flip-up feet to adjust its angle. Public reception of the keyboard was extremely positive, with some sources describing it as a major selling point of the PC and even as "the best keyboard available on any microcomputer."
![Bundesarchiv B 145 Bild-F077948-0006, Jugend-Computerschule mit IBM-PC](https://upload.wikimedia.org/wikipedia/commons/e/e9/Bundesarchiv_B_145_Bild-F077948-0006%2C_Jugend-Computerschule_mit_IBM-PC.jpg)
At release, IBM provided a
Game Control Adapter which offered a 15-pin port intended for the connection of up to two joysticks, each having two analog axes and two buttons.
Communications
Connectivity to other computers and peripherals was initially provided through serial and parallel ports.
IBM provided a serial card based on an
8250 UART
The 8250 UART (universal asynchronous receiver/transmitter) is an integrated circuit designed for implementing the interface for serial communications. The part was originally manufactured by the National Semiconductor Corporation. It was comm ...
. The BIOS supports up to two serial ports.
IBM provided two different options for connecting Centronics-compatible parallel printers. One was the IBM Printer Adapter, and the other was integrated into the MDA as the IBM Monochrome Display and Printer Adapter.
Expansion
![Personal_computer_-_Museo_scienza_tecnologia_Milano_14617_02](https://upload.wikimedia.org/wikipedia/commons/0/0a/Personal_computer_-_Museo_scienza_tecnologia_Milano_14617_02.jpg)
The expansion capability of the IBM PC was very significant to its success in the market. Some publications highlighted IBM's uncharacteristic decision to publish complete, thorough specifications of the system bus and memory map immediately on release, with the intention of fostering a market of compatible third-party hardware and software.
The motherboard includes five 62-pin card edge connectors which are connected to the CPU's I/O lines. IBM referred to these as "I/O slots," but after the expansion of the PC clone industry they became retroactively known as the
ISA bus
Industry Standard Architecture (ISA) is the 16-bit internal bus of IBM PC/AT and similar computers based on the Intel 80286 and its immediate successors during the 1980s. The bus was (largely) backward compatible with the 8-bit bus of the 80 ...
. At the back of the machine is a metal panel, integrated into the steel chassis of the system unit, with a series of vertical slots lined up with each card slot.
Most expansion cards have a matching metal bracket which slots into one of these openings, serving two purposes. First, a screw inserted through a tab on the bracket into the chassis fastens the card securely in place, preventing the card from wiggling out of place. Second, any ports the card provides for external attachment are bolted to the bracket, keeping them secured in place as well.
The PC expansion slots can accept an enormous variety of expansion hardware, adding capabilities such as:
* Graphics
* Sound
*
Mouse
A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus' ...
support
* Expanded memory
* Additional serial or parallel ports
* Networking
* Connection to proprietary industrial or scientific equipment
The market reacted as IBM had intended, and within a year or two of the PC's release the available options for expansion hardware were immense.
5161 Expansion Unit
The expandability of the PC was important, but had significant limitations.
One major limitation was the inability to install a hard drive, as described above. Another was that there were only five expansion slots, which tended to get filled up by essential hardware - a PC with a graphics card, memory expansion, parallel card and serial card was left with only one open slot, for instance.
IBM rectified these problems in the later XT, which included more slots and support for an internal hard drive, but at the same time released the 5161 Expansion Unit, which could be used with either the XT or the original PC. The 5161 connected to the PC system unit using a cable and a card plugged into an expansion slot, and provided a second system chassis with more expansion slots and a hard drive.
Software
![Digital Research CP-M-86 for the IBM Personal Computer Version 1](https://upload.wikimedia.org/wikipedia/commons/f/f2/Digital_Research_CP-M-86_for_the_IBM_Personal_Computer_Version_1.0_720x400.png)
IBM initially announced intent to support multiple operating systems:
CP/M-86
CP/M-86 was a version of the CP/M operating system that Digital Research (DR) made for the Intel 8086 and Intel 8088. The system commands are the same as in CP/M-80. Executable files used the relocatable .CMD file format. Digital Research als ...
,
UCSD p-System
UCSD Pascal is a Pascal programming language system that runs on the UCSD p-System, a portable, highly machine-independent operating system. UCSD Pascal was first released in 1977. It was developed at the University of California, San Diego (UCS ...
,
[ ] and an in-house product called
IBM PC DOS
IBM PC DOS, an acronym for IBM Personal Computer Disk Operating System, is a discontinued disk operating system for IBM PC compatibles. It was manufactured and sold by IBM from the early 1980s into the 2000s. Developed by Microsoft, it was also ...
, developed by
Microsoft
Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washing ...
.
In practice, IBM's expectation and intent was for the market to primarily use PC DOS,
CP/M-86 was not available for six months after the PC's release
and received extremely few orders once it was,
and p-System was also not available at release. PC DOS rapidly established itself as the standard OS for the PC and remained the standard for over a decade, with a variant being sold by Microsoft themselves as
MS-DOS
MS-DOS ( ; acronym for Microsoft Disk Operating System, also known as Microsoft DOS) is an operating system for x86-based personal computers mostly developed by Microsoft. Collectively, MS-DOS, its rebranding as IBM PC DOS, and a few ope ...
.
The PC included BASIC in ROM (four 8 KB chips), a common feature of 1980s home computers. Its ROM BASIC supported the cassette tape interface, but PC DOS did not, limiting use of that interface to BASIC only.
PC DOS version 1.00 supported only 160 KB SSDD floppies, but version 1.1, which was released nine months after the PC's introduction, supported 160 KB SSDD and 320 KB DSDD floppies. Support for the slightly larger nine sector per track 180 KB and 360 KB formats was added in March 1983.
Third-party software support grew extremely quickly, and within a year the PC platform was supplied with a vast array of titles for any conceivable purpose.(It used CUI based operating system BASIC to run the computer)
Reception
Reception of the IBM PC was extremely positive. Even before its release reviewers were impressed by the advertised specifications of the machine, and upon its release reviews praised virtually every aspect of its design both in comparison to contemporary machines and with regards to new and unexpected features.
Praise was directed at the build quality of the PC, in particular its keyboard, IBM's decision to use open specifications to encourage third party software and hardware development, their speed at delivering documentation and the quality therein, the quality of the video display, and the use of commodity components from established suppliers in the electronics industry.
The price was considered extremely competitive compared to the value per dollar of competing machines.
Two years after its release, BYTE Magazine retrospectively concluded that the PC had succeeded both because of its features – an 80-column screen, open architecture, and high-quality keyboard – and the failure of other computer manufacturers to achieve these features first:
''
Creative Computing
''Creative Computing'' was one of the earliest magazines covering the microcomputer revolution. Published from October 1974 until December 1985, the magazine covered the spectrum of hobbyist/home/personal computing in a more accessible format th ...
'' that year named the PC the best desktop computer between $2,000 and $4,000, praising its vast hardware and software selection, manufacturer support, and resale value.
Many IBM PCs remained in service long after their technology became largely obsolete. For instance, as of June 2006 (23–25 years after release) IBM PC and XT models were still in use at the majority of U.S.
National Weather Service
The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...
upper-air observing sites, processing data returned from
radiosondes
A radiosonde is a battery-powered telemetry instrument carried into the atmosphere usually by a weather balloon that measures various atmospheric parameters and transmits them by radio to a ground receiver. Modern radiosondes measure or calcula ...
attached to
weather balloon
A weather balloon, also known as sounding balloon, is a balloon (specifically a type of high-altitude balloon) that carries instruments aloft to send back information on atmospheric pressure, temperature, humidity and wind speed by means of a ...
s.
Due to its status as the first entry in the extremely influential PC industry, the original IBM PC remains valuable as a collector's item. , the system had a market value of $50–$500.
Model line
IBM sold a number of computers under the "Personal Computer" or "PC" name throughout the 80s. The name was not used for several years before being reused for the
IBM PC Series
The Personal Computer Series, or PC Series, was IBM's follow-up to the Personal System/2 and PS/ValuePoint. Announced in October 1994 and withdrawn in October 2000, it was replaced by the IBM NetVista, apart from the Pentium Pro-based PC360 an ...
in the 90s and early 2000s.
As with all PC-derived systems, all IBM PC models are nominally
software
Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
At the lowest programming level, executable code consists ...
-compatible, although some timing-sensitive software will not run correctly on models with faster CPUs.
Clones
Because the IBM PC was based on commodity hardware rather than unique IBM components, and because its operation was extensively documented by IBM, creating machines that were fully compatible with the PC offered few challenges other than the creation of a compatible BIOS ROM.
Simple duplication of the IBM PC BIOS was a direct violation of copyright law, but soon into the PC's life the BIOS was reverse-engineered by companies like
Compaq
Compaq Computer Corporation (sometimes abbreviated to CQ prior to a 2007 rebranding) was an American information technology company founded in 1982 that developed, sold, and supported computers and related products and services. Compaq produced ...
,
Phoenix Software Associates,
American Megatrends
AMI (American Megatrends International LLC, formerly American Megatrends Inc.) is an international hardware and software company, specializing in PC hardware and firmware. The company was founded in 1985 by Pat Sarma and Subramonian Shankar. It ...
and
Award
An award, sometimes called a distinction, is something given to a recipient as a token of recognition of excellence in a certain field. When the token is a medal, ribbon or other item designed for wearing, it is known as a decoration.
An awar ...
, who either built their own computers that could run the same software and use the same expansion hardware as the PC, or sold their BIOS code to other manufacturers who wished to build their own machines.
These machines became known as
IBM compatibles or "clones", and software was widely marketed as compatible with "IBM PC or 100% compatible". Shortly thereafter, clone manufacturers began to make improvements and extensions to the hardware, such as by using faster processors like the
NEC V20
The NEC V20 is a microprocessor that was designed and produced by NEC. It is both pin compatible and object code compatible with the Intel 8088, with an instruction set architecture (ISA) similar to that of the Intel 80188 with some extension ...
, which executed the same software as the 8088 at a higher speed up to 10 MHz.
The clone market eventually became so large that it lost its associations with the original PC and became a set of de facto standards established by various hardware manufacturers.
References
;Cited references
External links
IBM SCAMPIBM 5150 information at www.minuszerodegrees.netIBM PC 5150 System Disks and ROMsIBM PC from IT DictionaryIBM PC history and technical informationand collection of old digital and analog computers at oldcomputermuseum.com
IBM PC images and informationA brochure from November, 1982 advertising the IBM PC
{{DEFAULTSORT:Ibm Personal Computer
Personal Computer
A personal computer (PC) is a multi-purpose microcomputer whose size, capabilities, and price make it feasible for individual use. Personal computers are intended to be operated directly by an end user, rather than by a computer expert or tec ...
Computer-related introductions in 1981
Products introduced in 1981
16-bit computers
Products and services discontinued in 1987