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The IBM PC is 30

On 12 August 1981, the world changed

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IBM's PC predecessors

It has been claimed that the Chess' team's off-the-shelf approach was mandated by the limited development resources they were allowed, a sign that senior IBM executives saw no real future in the PC. Possibly so, and there were certainly time pressures: IBM management wanted the machine ready quickly, and Estridge and co appear to have been given a year to design the machine.

IBM Scamp

IBM's Scamp prototype
Source: Murple.net

But this was an approach IBM had taken before. In 1973, its General Systems Divison (GSD) embarked on 'Project Scamp', an effort to develop a single-user machine. Scamp stood for "Special Computer, APL Machine Portable" - the outcome was essentially a mobile personal computer-cum-calulator designed to run pre-loaded applications and allow user to write their own software using the APL language.

The Scamp team was given six-months in which to come up with a prototype. Ultimately, the result was the IBM 5100, a (barely) portable machine that weighted 23kg, had 16-64KB of storage depending on model, priced between $8975 and $19,975. It debuted in September 1975.

IBM 5100

Scamp follower: the IBM 5100
Source: Wikepedia

GSD maintained its interest in personal computer and, in July 1981, announced the System/23 Datamaster, a more PC-like machine than the 5100, but one still aimed at big business rather than individuals. The $9000 Datamaster was an all-in-one machine complete with keyboard, CRT display, 8-bit Intel 8085 processor and two 8in floppy disk drives.

The team at GSD developed the Datamaster using off-the-shelf components, most notably the Intel CPU. This choice seems to have influenced the Chess team, who eventually selected the 8088. They were familiar with the Datamaster endeavour: the 5150 would use the same expansion bus and add-in card slots as the GSD machine.

IBM System/23 Datamaster

The might-have-been PC: IBM's System/23 Datamaster
Source: Oldcomputers.net

The 5150's 8088 CPU was clocked at 4.77MHz and could be augmented with an optional 8087 maths co-processor. It had 16KB of memory and a 5.25in floppy drive - some models had two - for storage.

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