IBM PC 5150: the machine that created the standard (1981)

01 · THE BIRTHProject Chess

Before 1981 IBM sold computers almost exclusively to companies. In 1980 William Lowe, director of the Boca Raton laboratory, proposed to chief executive Frank Cary a computer for about 1,500 dollars, for small business and the home. Cary gave him a month for a prototype and a year for a finished product [1].

The project, code-named "Chess", was taken on by Don Estridge, who worked outside IBM's usual procedures. The motherboard was designed in 40 days, and in April 1981 production was taken over by the factory [1]. About half of the system (the bus, the display, the disk interface, the keyboard) was taken from the earlier IBM System/23 Datamaster. For the rest the team chose off-the-shelf parts: an Intel 8088 processor, an operating system from Microsoft, a printer from Epson [1]. It was also sold through shops, Sears and ComputerLand, not only through IBM's own dealers [1].

02 · THE MACHINEWhat is inside

The five slots soon proved too few: with a graphics card, extra memory, and parallel and serial ports, only one was left free [4]. This is one of the reasons for the next model, the XT.

03 · THE OPEN ARCHITECTUREThe documentation that changed the market

The team's most unexpected decision was to publish a technical reference with the schematics and the source code [1]. This let other companies make boards and programs without asking IBM. Within a year over 750 software packages came out for the PC, and dozens of manufacturers were selling memory cards [1].

• The bus. Mark Dean and Dennis Moeller created the bus that connects the disks and the printer [1]. IBM called the slots "I/O slots"; the name ISA appeared later, coined by the clone makers [4][9]. With the AT in 1984 the bus became 16-bit [9].
• The BIOS. The documentation was open, but the BIOS remained IBM's copyright; copying it was an infringement [4]. That is why compatible machines use a BIOS written from scratch using the "clean room" method [4][5].
• MS-DOS. Microsoft kept the right to license the system to other manufacturers too [5].

The profit did not stay with IBM. Its share of the personal computer market fell from about 80% in 1982–1983 to about 20% a decade later [1]. In 1987 IBM tried to regain control with the PS/2 and its own Micro Channel bus; competitors answered with the EISA standard [8].

04 · THE SOFTWAREWhat runs on the 5150

• PC DOS 1.0: the operating system came from Microsoft; it was later called MS-DOS [1]. The first floppies held 160 KB each [4].
• dBASE II: IBM commissioned a version for the PC, which was among the first programs at the launch in autumn 1981 [7]
• WordStar: created for CP/M; the first version for MS-DOS was 3.0 of April 1982. Until then many people bought a Z-80 card to use the CP/M version [7].
• Lotus 1-2-3: released on 26 January 1983; about 175,000 copies in the first year [6]. The spreadsheet, the charts and the database in one program gave the PC a reason to enter every accounts department.
• Turbo Pascal: released on 20 November 1983 for 49.95 dollars and sold by mail order [7].

05 · THE CLONESFrom Compaq to the Pravetz 16

The first IBM-compatible system was the Columbia MPC 1600 of June 1982 [5]. The Compaq Portable was announced in November 1982 and shipped in March 1983: an 8088 at 4.77 MHz, 128 KB of memory, 2,995 dollars, its own BIOS built by the "clean room" method [5]. It sold 53,000 units in its first year, with revenue of 111 million dollars [5]. Eagle and Corona also built their own computers, but IBM threatened them over the BIOS and they rewrote it [5].

In Bulgaria the team of engineer Ivan Marangozov at the Institute of Technical Cybernetics and Robotics of the Bulgarian Academy of Sciences began a 16-bit computer compatible with the IBM [3]. The Pravetz 16 (IMKO-4) had an 8088 processor at 4.77 MHz and 256 or 512 KB of memory, expandable to 640 KB [10]. The "A.Museum" gives two years: 1985 for the appearance of the machine and 1986 for the model in its list [3]. Production of the family continued until the collapse of the state system in 1990 [3]

06 · TIMELINEFrom 1980 to the PS/2

07 · THE LEGACYWhat remains

By the time Estridge died in 1985, over a million IBM PCs had been sold [2]. "Time" magazine named the PC "Machine of the Year" [1]. IBM sold its personal computer division to Lenovo in 2005 for 1.75 billion dollars [1].

The story is a lesson about open standards: the company that starts them does not always profit from them, but everyone who works on them does. The x86 architecture, which began with processors such as the 8088, is still the basis of mainstream desktop computers today.

Some of the dates and numbers above rest on a secondary source (Wikipedia) and are marked with the source number. That is why the page carries the label "updated", not "verified".

08 · SOURCESSources

1. IBM Heritage, "The IBM PC" (primary source, the manufacturer) — ibm.com/history/personal-computer
2. Computer History Museum, CHM Revolution, "The IBM PC" — computerhistory.org
3. A.Museum, "History of the Pravetz computers" (in Bulgarian), 10.08.2021 — amuseum.bg
4. Wikipedia, "IBM Personal Computer" (secondary) — en.wikipedia.org
5. Wikipedia, "Compaq Portable" (secondary) — en.wikipedia.org
6. Wikipedia, "Lotus 1-2-3" (secondary) — en.wikipedia.org
7. Wikipedia, "WordStar", "dBase", "Turbo Pascal" (secondary) — WordStar · dBase · Turbo Pascal
8. Wikipedia, "IBM Personal Computer XT", "IBM Personal Computer AT", "IBM PS/2" (secondary) — XT · AT · PS/2
9. Wikipedia, "Industry Standard Architecture" (secondary) — en.wikipedia.org
10. Wikipedia, "Pravetz" (secondary) — en.wikipedia.org/wiki/Pravetz_16

Checked on 03.10.2026. Prices are in dollars of the time. Translations from English are our own.

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