Z-80 SoftCard

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This was a plug-in card, supplied by Microsoft for use with the Apple II personal computer.

The Z80 SoftCard had a Zilog Z80 CPU. It was eventually renamed the Microsoft SoftCard.

It enabled the Apple II to run the CP/M operating system, developed by Digital Research, which was at the time an industry standard operating system for running business software on small computers.

This CP/M capability conferred by the Z80 SoftCard transformed the Apple II into a viable platform for running a much broader range of business software applications than had been possible up on the Apple II until that point.

The card was developed jointly between Tim Paterson of Seattle Computer Products SCP and a certain young Bill Gates and Don Burdis of Microsoft.

It was first demonstrated publicly at the West Coast Computer Faire in March 1980.

It may not be entirely unreasonable to claim that the Z80 SoftCard may have been perhaps the single most significant piece of computer hardware ever developed (certainly in the microcomputer era) because it seems to be the only product which would have prompted IBM to consider Microsoft, who were at the time exclusively a programming language vendor which had never developed an operating system before, as a contender for providing an operating system for IBM's forthcoming IBM PC when Digital Research themselves did not offer CP/M to IBM for this purpose.

The extent to which IBM's decision to approach Microsoft for the provision of the IBM PC operating system (a requirement which Microsoft did indeed eventually supply and which was called PC-DOS) might have been influenced by the Z80 SoftCard, remains tantalisingly undocumented, but as a persuasive case for this outcome, the SoftCard is unrivalled, simply because the feat of being able to run, by means of a surprisingly simple installation, the CPU of one type of computer inside a computer which was using a completely different CPU, running a completely different operating system, seemed at the time to be an extraordinary achievement.

As a result of this 'impression of operating system mastery' which the Softcard conferred upon Microsoft (especially in the eyes of IBM) it would have seemed inconceivable to IBM that a firm that was capable of delivering such a remarkable achievement was not at least as capable of delivering a perfectly serviceable CP/M-like operating system which could be used for IBM's Personal Computer.

Who, so the logic of the circumstances would seem to imply, would be expected to be more capable of delivering an operating system with 'CP/M capabilities' (i.e., suitability for running the majority of widely available business software applications) but running on a different CPU to the CPUs that CP/M ran on (CP/M ran on the Intel 8080 and the Zilog Z80 CPUs, whereas the IBM PC was going to use the Intel 8088 CPU)?

Who would have seemed to IBM at the time to have been more capable of delivering 'the IBM PC's equivalent of CP/M' than the people who had already succeeded in getting CP/M to run on an Apple II?

The Apple II was, after all a computer with a MOS Technology 6502 CPU, a CPU which was in many ways more different from the processors which ran CP/M than the new IBM's CPU would be from the Intel 8080 and the Zilog Z80.

So from IBM's perspective, it is conceivable that their requirements for what would become PC-DOS would potentially have seemed to have posed less of a challenge to Microsoft than the Z80 SoftCard.

This apparent 'ability to create exotic operating system hybrids' evidenced by the Z80 SoftCard, might have even made Microsoft seem to IBM to be even more suited to develop the new operating system than Digital Research, despite the fact that Digital Research had developed the industry standard microcomputer operating system and Microsoft did not.

Irrespective of the IBM perspective, many see the Softcard (and the associated project to develop it) as a critical and integral step in the development of DOS.

This is primarily because, from a development point of view, both the Softcard and DOS initially involved the same individuals 'travelling on the same development path' in the journey from the the 'pre-IBM' Intel (and Intel-compatible) microprocessor software support environment, to what followed in the IBM PC (and PC compatible) era.