IBM Personal Computer#Models

Prior to the 1980s, IBM had largely been known as a provider of business computer systems.{{Cite news|last=Pollack|first=Andrew|date=August 13, 1981|title=Big I.B.M.'s Little Computer|language=en-US|page=D1|work=The New York Times|url=https://www.nytimes.com/1981/08/13/business/big-ibm-s-little-computer.html|access-date=March 16, 2020|issn=0362-4331}} 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, Texas Instruments and Data General, and some large IBM customers were buying Apples.{{cite news|author=Morgan, Christopher P|date=March 1980|title=Hewlett-Packard's New Personal Computer|page=60|work=Byte|url=https://archive.org/stream/byte-magazine-1980-03/1980_03_BYTE_05-03_Computers_in_the_Labratory#page/n63/mode/2up|access-date=October 18, 2013}}{{cite news|author=Swaine, Michael|date=October 5, 1981|title=Tom Swift Meets the Big Boys: Small Firms Beware|page=45|work=InfoWorld|url=https://books.google.com/books?id=JT0EAAAAMBAJ&pg=RA1-PA45|access-date=January 1, 2015}}

As early as 1980 there were rumors of IBM developing a personal computer, possibly a miniaturized version of the IBM System/370,{{cite news|date=January 1981|title=Interest Group for Possible IBM Computer|page=313|work=Byte|url=https://archive.org/stream/byte-magazine-1981-01/1981_01_BYTE_06-01_Hand-held_Computers#page/n313/mode/2up|access-date=October 18, 2013}} and Matsushita acknowledged publicly that it had discussed with IBM the possibility of manufacturing a personal computer in partnership, although this project was abandoned.{{cite news|author=Libes, Sol|date=June 1981|title=IBM and Matsushita to Join Forces?|page=208|work=Byte|url=https://archive.org/stream/byte-magazine-1981-06/1981_06_BYTE_06-06_Operating_Systems#page/n209/mode/2up|access-date=October 18, 2013}}{{cite news|author=Morgan, Chris|date=July 1981|title=IBM's Personal Computer|page=6|work=Byte|url=https://archive.org/stream/byte-magazine-1981-07/1981_07_BYTE_06-07_Energy_Conservation#page/n7/mode/2up|access-date=October 18, 2013}} 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.{{cite web|date=January 23, 2003|title=IBM 5120|url=http://www-03.ibm.com/ibm/history/exhibits/pc/pc_6.html|archive-url=https://web.archive.org/web/20050311044344/http://www-03.ibm.com/ibm/history/exhibits/pc/pc_6.html|url-status=dead|archive-date=March 11, 2005|access-date=March 20, 2016|publisher=IBM}} As with other large computer companies, its new products typically required about four to five years for development,{{cite news|author=Morgan, Chris|date=January 1982|title=Of IBM, Operating Systems, and Rosetta Stones|page=6|work=Byte|url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n7/mode/2up|access-date=October 19, 2013}}{{cite news|author=Bunnell, David|date=Feb–Mar 1982|title=The Man Behind The Machine? / A PC Exclusive Interview With Software Guru Bill Gates|page=16|work=PC Magazine|url=https://books.google.com/books?id=w_OhaFDePS4C&pg=PA16|access-date=February 17, 2012}} 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."{{Cite web|date=January 23, 2003|title=IBM Archives: The birth of the IBM PC|url=https://www.ibm.com/ibm/history/exhibits/pc25/pc25_birth.html|access-date=October 3, 2020|website=www.ibm.com|language=en-US}}

IBM had previously produced microcomputers, such as 1975's IBM 5100, but targeted them towards businesses; the 5100 had a price tag as high as $20,000.{{cite web|title=Obsolete Technology Website|url=http://oldcomputers.net/ibm5100.html|access-date=August 14, 2008}} Their entry into the home computer market needed to be competitively priced.

In the summer of 1979, Ron Mion, IBM’s Senior Business Trends Advisor for entry-level systems, proposed a plan for IBM to enter the emerging microcomputer market. At that time, the likes of Apple and Tandy were starting to encroach on the small-business marketplace that IBM intended to dominate. Mion believed that that market would grow significantly and that IBM should aggressively pursue it. However, he felt that they wouldn’t be successful unless IBM departed from its long-standing business model.

Mion’s plan called for three major departures from how IBM traditionally did business. Mion felt that, if IBM wanted to compete in the microcomputer market, it would need to:

:a) Greatly reduce manufacturing costs by using standard, off-the-shelf components (e.g., disk drives, CRTs, power supplies, keyboards) in order to produce a competitively priced microcomputer

:b) Use a low-cost, third-party operating system. Mion felt that this was imperative in order to foster a cottage industry that could develop a broad array of applications that would help small businesses justify the purchase of a computer. Mion recommended Digital Research’s CP/M and a new O/S called MS-DOS from a little-known company named Microsoft.

:c) Allow its microcomputers to be sold and serviced by a distribution channel consisting of independent resellers. (At that time, IBM had been experimenting with a chain of IBM Business Systems Center storefronts but their least-expensive computer cost $14,000.)

That plan made its way up the chain of command but was ultimately rejected in the fall. The top IBM executives reaffirmed that all “IBM” computers, and their major components, must be developed, manufactured, sold, and serviced by IBM.

In January of 1980, Tandy released their Annual Report and, as was predicted in Mion's plan, it confirmed that their 1979 shipments had exceeded 100,000 TRS-80s (about $50 million worth). IBM quickly dusted off Mion’s marketing plan.

In 1980, IBM president John Opel, recognizing the value of entering this growing market, assigned William C. Lowe and Philip Don Estridge as heads of 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.{{cite book|author1=Blaxill, Mark|url=https://books.google.com/books?id=JO6kA0hebJIC&pg=PA195|title=The Invisible Edge: Taking Your Strategy to the Next Level Using Intellectual Property|author2=Eckardt, Ralph|publisher=Penguin Group|year=2009|isbn=9781591842378|pages=195–198}} Another source cites time pressure as the reason for the decision to use third-party components.{{cite book|title=Big Blues: The unmaking of IBM|author=Carroll, Paul|publisher=Random House|year=1993|isbn=0-517-88221-3|pages=22|url=https://archive.org/details/Big_Blues_The_Unmaking_IBM_Paul_Carroll}}

Atari proposed to IBM in 1980 that it act as original equipment manufacturer for an IBM microcomputer,{{cite web|author=Musil, Steven|date=October 28, 2013|title=William Lowe, the 'father of the IBM PC,' dies at 72|url=http://www.cnet.com/news/william-lowe-the-father-of-the-ibm-pc-dies-at-72/|access-date=January 8, 2015|publisher=CNet}} 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, 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.Atkinson, P, (2013) DELETE: A Design History of Computer Vapourware[http://www.paul-atkinson-design.com/#!design-history-of-computers] {{Webarchive|url=https://web.archive.org/web/20140301055854/http://www.paul-atkinson-design.com/#!design-history-of-computers|date=March 1, 2014}}, London: Bloomsbury Publishing.{{cite journal|author=Scott, Greg|date=October 1988|title="Blue Magic": A Review|url=https://books.google.com/books?id=WSBVAAAAMAAJ&pg=RA1-PA128|journal=U-M Computing News|volume=3|issue=19|pages=12–15}}

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.

The design process was kept under a policy of strict secrecy, with all other IBM divisions kept in the dark about the project.{{Cite web|title=IBM PC Announcement 1981|url=http://www.bricklin.com/ibmpcannouncement1981.htm|access-date=October 4, 2020|website=www.bricklin.com}}

Several CPUs were considered, including the Texas Instruments TMS9900, Motorola 68000 and Intel 8088. The 68000 had 32 bit registers with a flat 24 bit address space for up to 16MB of memory and was considered the best choice,{{Cite interview |last=Gates |first=Bill |interviewer=Michael J. Miller |title=Interview: Bill Gates, Microsoft |url=http://www.pcmag.com/article/0,2997,s=1754&a=11072,00.asp |date=March 25, 1997 |archive-url=https://web.archive.org/web/20010823113747/http://www.pcmag.com/article/0%2C2997%2Cs%3D1754%26a%3D11072%2C00.asp |archive-date=August 23, 2001 |access-date=September 4, 2020 |url-status=live |work= PC Magazine}} but was not production-ready like the others.{{Cite news |last=Rhines |first=Walden C. |author-link=Walden C. Rhines |date=June 22, 2017 |title=The Inside Story of Texas Instruments' Biggest Blunder: The TMS9900 Microprocessor |language=en |work=IEEE Spectrum |url=https://spectrum.ieee.org/the-inside-story-of-texas-instruments-biggest-blunder-the-tms9900-microprocessor |access-date=July 8, 2017}} The IBM 801 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{{dubious|date=February 2024|reason=According to wiki page IBM 801 the processor wasn't production ready either}}. The TMS9900 had only 16 bits of address space which was the same as other 8 bit chips and was rejected as it was inferior to the Intel 8088 which had 20 bits of address space which could use one megabyte of memory.{{cite web | url=https://spectrum.ieee.org/the-inside-story-of-texas-instruments-biggest-blunder-the-tms9900-microprocessor | title=The Inside Story of Texas Instruments' Biggest Blunder: The TMS9900 Microprocessor - IEEE Spectrum }}

The Intel 8086 architecture had 16 bit registers and used a segment scheme to increase the address space to 20 bits or 1MB of memory which complicated programming but was a big step up from 64K limit of most 8 bit chips. The 8086 was designed as a source code compatible, though not binary compatible, extension of the older 8080 which made it easier to port existing software like BASIC. IBM chose the 8088 variant of the 16 bit 8086 because Intel offered a better price for the former and could provide more units,{{cite news|author=Freiberger, Paul|date=August 23, 1982|title=Bill Gates, Microsoft and the IBM Personal Computer|page=22|work=InfoWorld|url=https://books.google.com/books?id=VDAEAAAAMBAJ&pg=PA22|access-date=January 29, 2015}} 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 62-pin expansion bus slots were also designed to be similar to the Datamaster slots,{{cite web|url=https://www.edn.com/whence-came-the-ibm-pc/|title=Whence Came the IBM PC|website=edn.com|date=September 15, 2001|access-date=October 13, 2020|author=John Titus}} and its keyboard design and layout became the Model F keyboard shipped with the PC,{{cite news | url=https://archive.org/stream/byte-magazine-1990-09/1990_09_BYTE_15-09_15th_Anniversary_Summit#page/n451/mode/2up | title=The Creation of the IBM PC | work=Byte | date=September 1990 | access-date=April 2, 2016 | author=Bradley, David J. | pages=414–420}} but otherwise the PC design differed in many ways.

The 8088 motherboard was designed in 40 days,{{Cite news|title=Remembering the Beginning|work=PC Magazine|url=http://www.pcmag.com/article/0,2997,s=1754&a=11072,00.asp|url-status=dead|archive-url=https://web.archive.org/web/20020206040238/http://www.pcmag.com/article/0%2C2997%2Cs%3D1754%26a%3D11072%2C00.asp|archive-date=February 6, 2002|access-date=September 4, 2020}} with a working prototype created in four months,{{Cite news|last=Sanger|first=David E.|date=August 5, 1985|title=Philip Estridge Dies in Jet Crash; Guided Ibm Personal Computer|language=en-US|work=The New York Times|url=https://www.nytimes.com/1985/08/05/us/philip-estridge-dies-in-jet-crash-guided-ibm-personal-computer.html|access-date=October 4, 2020|issn=0362-4331}} demonstrated in January 1981. The design was essentially complete by April 1981, when it was handed off to the manufacturing team.{{Cite web|date=January 23, 2003|title=IBM Archives: The birth of the IBM PC|url=https://www.ibm.com/ibm/history/exhibits/pc25/pc25_birth.html|access-date=October 4, 2020|website=www.ibm.com|language=en-US}} 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; the printer was manufactured by Epson.{{Cite book|url=https://books.google.com/books?id=WSBVAAAAMAAJ&pg=RA1-PA128|title=U-M Computing News|date=1988|publisher=Computing Center|language=en}}{{fv|date=July 2023}} Because none of the functional components were designed by IBM, they obtained only a handful of patents on the PC, covering such features as the bytecoding for color monitors, DMA access operation, and the keyboard interface. They were never enforced.{{Cite magazine|magazine=InfoWorld|url=https://books.google.com/books?id=VDAEAAAAMBAJ|page=[https://books.google.com/books?id=VDAEAAAAMBAJ&pg=PA29 21]|date=August 23, 1982|title=Let's Keep Those Systems Open|publisher=InfoWorld Media Group, Inc.|language=en|via=Google Books}}

Many of the designers were computer hobbyists who owned their own computers,{{r|morgan198201}} including many Apple II owners, which influenced the decisions to design the computer with an open architecture{{cite news | url=https://books.google.com/books?id=Pq3POofPsBEC | title=Ostracized PC1 Designer Still Ruminates 'Why?' | work=PC Magazine | date=September 18, 1984 | access-date=October 25, 2013 | author=Porter, Martin | page=33}} and publish technical information so others could create compatible software and expansion slot peripherals.{{Cite magazine |last=Greenwald |first=John |date=July 11, 1983 |title=The Colossus That Works |url=http://content.time.com/time/magazine/article/0,9171,949693-2,00.html |url-status=live |url-access=subscription | magazine=TIME |archive-url=https://web.archive.org/web/20080514004334/http://www.time.com/time/magazine/article/0,9171,949693-2,00.html |archive-date=May 14, 2008 |access-date=May 18, 2019}}

During the design process IBM avoided vertical integration as much as possible, for example choosing to license Microsoft BASIC rather than utilizing the in-house version of BASIC used for mainframes due to the better existing public familiarity with the Microsoft version.{{cite news|author=Curran, Lawrence J.|last2=Shuford, Richard S.|date=November 1983|title=IBM's Estridge|pages=88–97|work=Byte|url=https://archive.org/stream/byte-magazine-1983-11/1983_11_BYTE_08-11_Inside_the_IBM_PC#page/n89/mode/2up|access-date=March 19, 2016}}

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, keyboard, and no disk drives. The price was designed to compete with comparable machines in the market.{{cite web|date=January 23, 2003|title=The birth of the IBM PC|url=http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_birth.html|archive-url=https://web.archive.org/web/20060814072714/http://www-03.ibm.com/ibm/history/exhibits/pc25/pc25_birth.html|url-status=dead|archive-date=August 14, 2006|access-date=June 13, 2014|publisher=IBM Archives}} For comparison, the Datamaster, announced two weeks earlier as IBM's least expensive computer, cost $10,000.{{Cite news| last1 = Pollack | first1 = Andrew |date=March 27, 1983|title=Big I.B.M. Has Done It Again| language=en-US | work = The New York Times | url = https://www.nytimes.com/1983/03/27/business/big-ibm-has-done-it-again.html|access-date=October 4, 2020|issn=0362-4331 | df = dmy-all}}

IBM's marketing campaign licensed the likeness of Charlie Chaplin's character "The Little Tramp" for a series of advertisements based on Chaplin's movies, played by Billy Scudder.{{cite journal|author=Papson, Stephen|date=April 1990|title=The IBM tramp|url=http://www.ejumpcut.org/archive/onlinessays/JC35folder/IBMtramp.html|journal=Jump Cut: A Review of Contemporary Media|issue=35|pages=66–72}}

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 and Sears, who provided important knowledge of the marketplace{{cite news|author=Mace, Scott|date=October 5, 1981|title=Where You Can Go to Purchase the New Computers|page=49|work=InfoWorld|url=https://books.google.com/books?id=JT0EAAAAMBAJ&pg=RA1-PA49|access-date=January 1, 2015}}{{cite news | url=http://www.atarimagazines.com/creative/v10n11/298_IBM_colossus_of_Armonk.php | title=IBM: Colossus of Armonk | work=Creative Computing | date=November 1984 | access-date=February 26, 2013 | author=Sandler, Corey | page=298}}{{cite news | url=https://hbr.org/1989/07/new-ventures-lessons-from-xerox-and-ibm | title=New Ventures: Lessons from Xerox and IBM | work=Harvard Business Review | date=July 1989 | access-date=January 20, 2015 | author=Elder, Tait}}{{cite news | url=https://books.google.com/books?id=UCIvSU6Y2GAC | title=Apple Charts The Course For IBM | work=PC Magazine | date=February 21, 1984 | access-date=October 24, 2013 |author1=McMullen, Barbara E. |author2=John F. | page=122}} 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.{{cite news|date=Feb–Mar 1982|title=Billion Dollar Baby|page=5|work=PC|url=https://books.google.com/books?id=w_OhaFDePS4C&pg=PA5|access-date=February 25, 2016}} After release, IBM's PC immediately became the talk of the entire computing industry.{{cite news|author=Bunnell, David|date=February 3, 1982|title=Flying Upside Down|page=10|work=PC Magazine|url=https://books.google.com/books?id=w_OhaFDePS4C&pg=PA10|access-date=April 6, 2014}} 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.{{cite news|author1=Edlin, Jim|author2=Bunnell, David|date=February–March 1982|title=IBM's New Personal Computer: Taking the Measure / Part One|page=42|work=PC Magazine|url=https://books.google.com/books?id=w_OhaFDePS4C&pg=PA42|access-date=October 20, 2013}}

Sales exceeded IBM's expectations by as much as 800% (9x), with the company at one point shipping as many as 40,000 PCs per month.{{cite news|author=Hayes, Thomas C.|date=October 24, 1983|title=Eagle Computer Stays in the Race|work=The New York Times|url=https://www.nytimes.com/1983/10/24/business/eagle-computer-stays-in-the-race.html|access-date=January 10, 2015}} IBM estimated that home users made up 50 to 70% of purchases from retail stores.{{cite news|author=Burton, Kathleen|date=March 1983|title=Anatomy of a Colossus, Part III|page=467|work=PC|url=https://books.google.com/books?id=7wCiNAUEuAMC&pg=RA1-PA467|access-date=March 30, 2014}} In 1983, IBM sold more than 750,000 machines,{{Cite web|date=August 12, 2006|title=Origin of the IBM PC|url=https://lowendmac.com/2006/origin-of-the-ibm-pc/|access-date=October 4, 2020|website=Low End Mac|language=en-US}} while Digital Equipment Corporation, one of the companies whose success had spurred IBM to enter the market, sold only 69,000.{{cite news |author=Ahl, David H. |author-link=David H. Ahl |date=March 1984 |title=Digital |pages=38–41 |work=Creative Computing |url=https://archive.org/stream/creativecomputing-1984-03/Creative_Computing_v10_n03_1984_Mar#page/n39/mode/2up |access-date=February 6, 2015}}

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.{{cite news|author1=Watt, Peggy|author2=McGeever, Christine|date=January 14, 1985|title=Macintosh Vs. IBM PC At One Year|pages=16–17|work=InfoWorld|url=https://books.google.com/books?id=-i4EAAAAMBAJ&pg=PA15|access-date=December 28, 2014}} Hardware support also grew rapidly, with 30–40 companies competing to sell memory expansion cards within a year.{{cite news|author=Markoff, John|date=August 23, 1982|title=Competition and innovation mark IBM add-in market|page=20|work=InfoWorld|url=https://books.google.com/books?id=VDAEAAAAMBAJ&pg=PA20|access-date=January 29, 2015}}

By 1984, IBM's revenue from the PC market was $4 billion, more than twice that of Apple.{{cite news|author=Libes, Sol|date=September 1985|title=The Top Ten|page=418|work=Byte|url=https://archive.org/stream/byte-magazine-1985-09/1985_09_BYTE_10-09_Homebrewing#page/n401/mode/2up|access-date=October 27, 2013}} 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.{{Cite book|url=https://archive.org/stream/byte-magazine-1984-09/1984_09_BYTE_09-09_Guide_to_the_IBM_PCs#page/n33/mode/2up|title=Byte Magazine Volume 09 Number 09 - Guide to the IBM PCs|date=Sep 1984}} A 1985 Fortune survey found that 56% of American companies with personal computers used PCs while 16% used Apple.{{cite magazine | url=https://books.google.com/books?id=Pq3POofPsBEC | title=Ostracized PC1 Designer Still Ruminates 'Why?' | magazine=PC Magazine |volume=3| issue=18| date=September 18, 1984 | access-date=October 25, 2013 | author=Porter, Martin | page=33 |via=Google Books}}

Almost as soon as the PC reached the market, rumors of hardware and software compatible clones began,{{cite news|date=February–March 1982|title=PCommuniques|page=5|work=PC Magazine|url=https://books.google.com/books?id=w_OhaFDePS4C&pg=PA5|access-date=October 20, 2013}} and the first legal PC-compatible clone—the MPC 1600 by Columbia Data Products—was released in June 1982, less than a year after the PC's debut.{{cite book | last=Rohlfs | first=Jeffrey H. | date=2003 | url=https://books.google.com/books?id=rmFag8P4CF8C | title=Bandwagon Effects in High-technology Industries | publisher=MIT Press | page=122 | isbn=9780262681384 | via=Google Books}}

Eventually, IBM sold its PC business to Lenovo in 2004.

File:Ibm 5150 inthebox edit.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.{{Cite book|last=Henderson|first=Harry|url=https://books.google.com/books?id=3Tla6d153uwC&q=ibm%20pc%20open%20standards&pg=PA236|title=Encyclopedia of Computer Science and Technology|date=2009|publisher=Infobase Publishing|isbn=978-1-4381-1003-5|pages=236|language=en}}

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:

The PC is built around a single large circuit board called a motherboard 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 PIC, an Intel 8237 DMA controller, and an Intel 8253 PIT. The PIT provides {{nowrap|18.2 Hz}} clock "ticks" and dynamic memory refresh timing.

File:IBM PC Motherboard (1981).jpg

File:Ibm5150mobo1984black.jpg

The CPU is an Intel 8088, a cost-reduced form of the Intel 8086 which largely retains the 8086's internal 16-bit logic, but exposes only an 8-bit bus.{{Cite book|url=https://archive.org/stream/byte-magazine-1981-10/1981_10_BYTE_06-10_Local_Networks#page/n31/mode/2up|title=Byte Magazine Volume 06 Number 10 - Local Networks|date=October 1981|pages=28–34}} The CPU is clocked at 4.77 MHz; clones and later PC models have higher CPU speeds that break compatibility with software developed for the original PC.{{Cite book|last=Graves|first=Michael W.|url=https://books.google.com/books?id=GZFv0Vv8CEcC&q=%22turbo%20button%22%20crash&pg=PA66|title=A+ Guide to PC Hardware Maintenance and Repair|date=September 17, 2004|publisher=Cengage Learning|isbn=978-1-4018-5230-6|language=en}} The single base clock frequency for the system is 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, yields the required 3.579545 MHz for the NTSC color carrier frequency.

The PC motherboard includes 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 math coprocessor, which improves floating-point math performance.{{Cite book|url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n41/mode/2up|title=Byte Magazine Volume 07 Number 01 - The IBM Personal Computer|date=January 1982}}

PC mainboards were manufactured with the first memory bank of initially Mostek 4116-compatible,[https://minuszerodegrees.net/memory/4116.htm 4116 class RAM] One bank used nine of these chips (eight 16-kilobit chips = 16 kilobytes, plus one chip for parity). or later 4164-compatible[https://minuszerodegrees.net/memory/4164.htm 4164 class RAM] – One bank used nine of these chips (eight 64-kilobit chips = 64 kilobytes, plus one chip for parity). DIP DRAMs soldered to the board,{{cite web | url=https://minuszerodegrees.net/5150/ram/5150_ram.htm | title=Minuszerodegrees.net }} for a minimum configuration of first just 16 KB, or later 64 KB of RAM. Memory upgrades from IBM and third parties provide socketed installation in three further onboard banks, and as ISA expansion cards.

The first 400,000 16 KB mainboards ("16KB-64KB" ID) sold until March 1983 can be upgraded to a maximum of 64 KB onboard without using slots, and the later 64 KB revision ("64KB-256KB" ID) to a maximum of 256 KB on the motherboard.{{Cite magazine |last=Feldmann |first=Peter |date=1985-10-01 |title=Upgrading Your 64K PC |url=https://archive.org/details/PC-Mag-1985-10-01/page/n146/mode/1up?view=theater |access-date=2025-04-13 |magazine=PC |pages=145-149}} RAM cards can upgrade either variant further, for a total of 640 KB conventional memory, and possibly several megabytes of expanded memory beyond that, though on PC/XT-class machines, the latter was a very expensive third-party hardware option only available later in the IBM 5150's lifecycle and only usable with dedicated software support (i.e. only accessible via a RAM window in the Upper Memory Area{{cite web|url=https://minuszerodegrees.net/5150/misc/5150%20-%20Memory%20Map%20of%20the%20640%20KB%20to%201%20MB%20Area.jpg|title=IBM 5150 - Memory Map of the 640 KB to 1 MB Area (the 'Upper Memory Area')|website=minuszerodegrees.net|archive-url=https://web.archive.org/web/20250409172823/https://minuszerodegrees.net/5150/misc/5150%20-%20Memory%20Map%20of%20the%20640%20KB%20to%201%20MB%20Area.jpg|archive-date=9 April 2025|url-status=live}}); this was relatively rarely equipped and utilized on the original IBM PC, much less fully so, thus the machine's maximum RAM configuration as commonly understood is 640 KB.

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, with the dates 04/24/81, 10/19/81, and 10/27/82 (the first to boot from hard disk). The company offered an upgrade kit.{{r|feldmann19851001}}

File:IBM PC 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 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, 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{{cite news|author=Williams, Gregg|date=January 1982|title=A Closer Look at the IBM Personal Computer|page=36|work=Byte|url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n37/mode/2up|access-date=October 19, 2013}} and was not released until March 1983.{{cite web |publisher=IBM |type=Announcement letter |id=183-002 |title=IBM Color Display, 5153 Model 1 For IBM Personal Computer |date=February 4, 1983 |url=https://www.ibm.com/docs/en/announcements/archive/ENUS183-002}}

MDA scanned at a higher frequency and required a proprietary monitor, the IBM 5151. The card also included a built-in printer port.{{Cite book|url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n37/mode/2up|title=Byte Magazine Volume 07 Number 01 - The IBM Personal Computer|date=January 1982}}

Both cards could also be installed simultaneously for mixed graphics and text applications.{{Cite web|title=Dual-Head operation on vintage PCs|url=https://www.seasip.info/VintagePC/dualhead.html|access-date=August 16, 2020|website=www.seasip.info}} For instance, AutoCAD, Lotus 1-2-3 and other software allowed use of a CGA Monitor for graphics and a separate monochrome monitor for text menus. Third parties went on to provide an enormous variety of aftermarket graphics adapters, such as the Hercules Graphics Card.

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.

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,{{Cite book|title=The Peter Norton Programmer's Guide to the IBM PC|publisher=Microsoft Corporation|year=1985|isbn=0914845462|quote=I have never encountered a PC program on tape for sale. In fact, about the only use of the cassette port that I am aware of is the homespun and jerry-rigged use of this port as a poor-man's serial port.}} probably because very few PCs were sold without floppy drives. The port was removed on the very next PC model, the XT.{{Cite book|last=Robert|first=Brenner|title=IBM Personal Computer: Troubleshooting & Repair for the IBM PC, PC/XT, and PC AT|publisher=Sams|year=1989|isbn=0672226626|quote=Next to the keyboard connector is a 5-pin circular connector for cassette data input/output. This connection is not available on the XT or AT.}}

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.{{Cite web|title=minuszerodegrees.net|url=http://www.minuszerodegrees.net/5150/hdd/5150_hard_drive_support.htm|access-date=October 3, 2020|website=www.minuszerodegrees.net}}

Although official hard drive support did not exist, the third party market did provide early hard drives that connected to the floppy disk controller{{Citation needed|date=December 2022}}, but required a patched version of PC DOS to support the larger disk sizes.

File:IBM Model F XT.png keyboard]]

The only option for human interface 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 keyboards 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."

File:Bundesarchiv B 145 Bild-F077948-0006, Jugend-Computerschule mit IBM-PC.jpg monitor (model 5153), original keyboard, 5152 printer and paper stand (1988)]]

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. (The early PCs predated the advent of the "Windows, Icons, Mouse, Pointer" concept and so did not have a mouse.)

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 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.

{{refimprove|section|date=August 2021}}

File: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.{{Cite book|url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n57/mode/2up|title=Byte Magazine Volume 07 Number 01 - The IBM Personal Computer|date=January 1982}}

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. 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 support
• Expanded memory
• Joystick port
• 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.

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.

File:IBM 5154 - PC DOS Prompt.jpg

File:Digital Research CP-M-86 for the IBM Personal Computer Version 1.0 720x400.png CP/M-86 Version 1.0 for the IBM PC]]

IBM initially announced intent to support multiple operating systems: CP/M-86, UCSD p-System,{{Cite book|url=https://archive.org/stream/byte-magazine-1982-01/1982_01_BYTE_07-01_The_IBM_Personal_Computer#page/n41/mode/2up|title=Byte Magazine Volume 07 Number 01 - The IBM Personal Computer|date=January 1982}} {{verify source |date=November 2020 |reason=This ref was deleted Special:Diff/990243364 by a bug in VisualEditor and later restored by a bot from the original cite located at Special:Permalink/990243296 cite #62 - verify the cite is accurate and delete this template. User:GreenC_bot/Job_18}} and an in-house product called IBM PC DOS, based on 86-DOS from Seattle Computer Products and provided by Microsoft.{{cite news|author=Freiberger, Paul|date=October 5, 1981|title=Some Confusion at the Heart of IBM Microcomputer / Which Operating System Will Prevail?|pages=50–51|work=InfoWorld|url=https://books.google.com/books?id=JT0EAAAAMBAJ&pg=RA1-PA50|access-date=January 1, 2015}}{{r|morgan198201}} In practice, IBM's expectation and intent was for the market to primarily use PC DOS.{{cite news | url=https://books.google.com/books?id=w_OhaFDePS4C | title=Boca Diary | work=PC Magazine | date=April–May 1982 | access-date=October 21, 2013 | author=Bunnell, David | page=22}} CP/M-86 was not available for six months after the PC's release{{cite news|author=Edlin, Jim|date=June–July 1982|title=CP/M Arrives|page=43|work=PC Magazine|url=https://books.google.com/books?id=w_OhaFDePS4C&pg=RA2-PA43|access-date=October 21, 2013}} and received extremely few orders once it was,{{cite news|date=February 1983|title=PCommuniques|page=53|work=PC Magazine|url=https://books.google.com/books?id=7wCiNAUEuAMC&pg=PA53|access-date=October 21, 2013}} 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.

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.

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.{{cite news | url=https://archive.org/stream/byte-magazine-1981-10/1981_10_BYTE_06-10_Local_Networks#page/n27/mode/2up | title=The IBM Personal Computer / First Impressions | work=Byte | date=October 1981 | access-date=October 19, 2013 | author=Lemmons, Phil | page=36}} 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:

{{Blockquote|In retrospect, it seems IBM stepped into a void that remained, paradoxically, at the center of a crowded market.{{cite news | url=https://archive.org/stream/byte-magazine-1984-09/1984_09_BYTE_09-09_Guide_to_the_IBM_PCs#page/n3/mode/2up | title=IBM and Its Personal Computers | work=Byte | date=Fall 1984 | access-date=18 March 2016 | author=Lemmons, Phil | page=1}}}}

Creative Computing 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.{{Cite magazine |last=Ahl |first=David H. |author-link=David H. Ahl |date=December 1984 |title=Top 12 computers of 1984 |url=https://www.atarimagazines.com/creative/v10n12/10_Top_12_computers_of_1984.php |magazine=Creative Computing |access-date=March 16, 2019}}

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 upper-air observing sites, processing data returned from radiosondes attached to weather balloons.

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. {{As of|2007}}, the system had a market value of $50–$500.{{cite web|last1=McCracken|first1=Harry|date=August 27, 2007|title=The Most Collectible PCs of All Time|url=https://www.pcworld.com/article/136242/article.html|access-date=September 25, 2017|website=PCWorld|language=en|archive-date=August 22, 2017|archive-url=https://web.archive.org/web/20170822070004/http://www.pcworld.com/article/136242/article.html|url-status=dead}}

{{See also|List of IBM Personal Computer models}}

IBM sold a number of computers under the "Personal Computer" or "PC" name throughout the 1980s. The name was not used for several years before being reused for the IBM PC Series in the 1990s and early 2000s. The PC line was replaced by the next generation IBM PS/2 in 1987 which introduced new hardware standards incompatible with those previously established by IBM and adopted in the IBM PC compatible industry. The IBM PC Series returned to the ISA standard hardware and was replaced by the IBM NetVista, which in turn was replaced by ThinkCentre models in 2003. IBM Personal Systems Group was sold to Lenovo in 2005.

As with all PC-derived systems, all IBM PC models are nominally software-compatible, although some timing-sensitive software will not run correctly on models with faster CPUs.

{{main|Influence of the IBM PC on the personal computer market}}

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, Phoenix Software Associates, American Megatrends and Award, 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, 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.

{{Timeline of the IBM Personal Computer}}

;Cited references

{{Reflist|30em}}

{{Commons category}}

• [https://www.youtube.com/watch?v=L_BWL7vCaa0 IBM SCAMP]
• [http://www.minuszerodegrees.net IBM 5150 information at www.minuszerodegrees.net]
• [http://www.theoldcomputer.com/roms/index.php?folder=IBM/PC-5150 IBM PC 5150 System Disks and ROMs]
• [https://archive.today/20130506223315/http://www.itdictionary.org/term/IBM_PC.aspx IBM PC from IT Dictionary]
• [https://www.old-computers.com/museum/computer.asp?c=274 IBM PC history and technical information]
• [http://lowendmac.com/orchard/06/0811.html What a legacy! The IBM PC's 25 year legacy]
• [http://www.cnn.com/2006/TECH/biztech/08/11/ibmpcanniversary/index.html CNN.com - IBM PC turns 25]
• [http://www.oldcomputermuseum.com/ibm_5150.html IBM-5150] and collection of old digital and analog computers at oldcomputermuseum.com
• [http://www.vintage-computer.com/ibm_pc.shtml IBM PC images and information] {{Webarchive|url=https://web.archive.org/web/20060705211337/http://www.vintage-computer.com/ibm_pc.shtml |date=July 5, 2006 }}
• [http://digitize.textfiles.com/items/1982-ibm-personal-computer/ A brochure from November, 1982 advertising the IBM PC]
• [http://www.corestore.org/XT370-1.jpg A Picture of the XT/370 cards, showing the dual 68000 processors ] {{Webarchive|url=https://web.archive.org/web/20211218053755/http://www.google.com/imgres?imgurl=http%3A%2F%2Fwww.corestore.org%2FXT370-1.jpg&imgrefurl=http%3A%2F%2Fdomino.research.ibm.com%2Fcomm%2Fresearch_people.nsf%2Fpages%2Fkoved.history.html&usg=__hfms9QIM7ODhMa7oycO3YzpCSr4%3D&h=1680&w=2240&sz=1107&hl=en&start=24&zoom=1&tbnid=oczfii5c6zO6KM%3A&tbnh=127&tbnw=153&ei=NTZkTdyCKYu4sQPP6cTdCA&prev=%2Fimages%3Fq%3DIBM%2BAT%2F370%26um%3D1%26hl%3Den%26sa%3DN%26biw%3D1355%26bih%3D744%26tbs%3Disch%3A10%2C811&um=1&itbs=1&iact=hc&vpx=632&vpy=213&dur=6215&hovh=194&hovw=259&tx=62&ty=219&oei=HTZkTfDHBpPksQP51PHCCA&page=2&ndsp=28&ved=1t%3A429%2Cr%3A17%2Cs%3A24&biw=1355&bih=744 |date=December 18, 2021 }}
• [https://bitsavers.org/pdf/ibm/pc/GG24-3057-00_IBM_PC_Internals_Fundamentals_Course_Notes_198603.pdf IBM PC Internals Fundamentals Course Notes] (PDF)

{{IBM}}

{{IBM personal computers}}

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Personal Computer

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