Editing IBM Personal Computer (section)

=== 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.<ref>{{Cite web|title=IBM PC Announcement 1981|url=http://www.bricklin.com/ibmpcannouncement1981.htm|access-date=October 4, 2020|website=www.bricklin.com}}</ref>

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,<ref name="millergates200119970325">{{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&amp;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= [[PCMag|PC Magazine]]}}</ref> but was not production-ready like the others.<ref name="rhines20170622">{{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}}</ref> 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 [[Commercial off-the-shelf |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.<ref>{{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 }}</ref>

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 [[Intel 8086|8086]] because Intel offered a better price for the former and could provide more units,<ref name="freiberger19820823">{{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}}</ref> 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,<ref>{{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}}</ref> and its keyboard design and layout became the [[IBM Model F|Model F]] keyboard shipped with the PC,<ref name="bradley199009">{{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 (magazine)|Byte]] | date=September 1990 | access-date=April 2, 2016 | author=Bradley, David J. | pages=414–420}}</ref> but otherwise the PC design differed in many ways.

The 8088 motherboard was designed in 40 days,<ref>{{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}}</ref> with a working prototype created in four months,<ref name=nyt>{{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}}</ref> demonstrated in January 1981. The design was essentially complete by April 1981, when it was handed off to the manufacturing team.<ref>{{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}}</ref> 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]].<ref>{{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}}</ref>{{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.<ref name="R.Turner one attorney who obtained these patents for IBM.">{{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}}</ref>

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]]<ref name="porter19840918">{{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}}</ref> and publish technical information so others could create compatible software and [[expansion slot]] peripherals.<ref name="greenwald19830711">{{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}}</ref>

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.<ref name="byte198311">{{cite news|author=Curran, Lawrence J.|last2=Shuford, Richard S.|date=November 1983|title=IBM's Estridge|pages=88–97|work=[[Byte (magazine)|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}}</ref>