The Z-80 SoftCard was a plug-in card supplied by Microsoft for use with the Apple II personal computer, which did not have a Z-80 compatible processor and could not run CP/M. It had a Zilog Z80 CPU plus some 74LS00 series TTL chips to adapt that processor's bus to the rather different bus system used in the Apple. The card was eventually renamed the Microsoft SoftCard.
Microsoft's first hardware product, it enabled the Apple II to run the Digital Research CP/M operating system, at the time an industry-standard operating system for running business software and many compilers and interpreters for several high-level languages on microcomputers. CP/M, one of the earliest cross-platform operating systems, was easily adaptable to a wide range of auxiliary chips and peripheral hardware, but it required an Intel 8080-compatible CPU, which the Zilog Z80 was, but which the Apple's CPU, the MOS Technology 6502, wasn't.
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 until then.
The SoftCard was Paul Allen's idea and was developed jointly between Tim Paterson of Seattle Computer Products (SCP) and Bill Gates and Don Burtis of Microsoft, after SCP developed the initial prototypes. Microsoft received most of its revenue from selling language compilers and interpreters for CP/M systems at this time, which was before Microsoft's MS-DOS operating system (for 8086-compatible processors as used by the IBM PC and other microcomputers) was introduced and became the company's best-selling product. A copy of the Microsoft BASIC programming language was included in the Softcard package. It was first demonstrated publicly at the West Coast Computer Faire in March 1980.
It was an immediate success; 5,000 cards, a large number given the microcomputer market at the time, were purchased in the initial three months at $349 each, and the card sold well for several years. The SoftCard was the single most popular platform to run CP/M. As Steve Ballmer stated during the Microsoft Surface reveal, the SoftCard was Microsoft's number one revenue source in 1980.
- Lock, Robert (May-June 1980). "An Apple Breakthru". Compute!. p. 6. Retrieved 25 October 2013.
- Hogan, Thom (March 3, 1981). "Microsoft's Z80 SoftCard". Infoworld (Popular Computing) 3 (4): pp. 20–21. ISSN 0199-6649.
- Raburn, Vern (October 20, 1980). "Letters: Developed by Microsoft". Computerworld 14 (43): p. 37. ISSN 0010-4841. "It was one of the founders of Microsoft, Paul Allen, who hit upon the idea of putting a Z80 processor into the Apple."
- William H. Gates IV Page Voteview.com
- Freiberger, Paul; Swaine, Michael (2000). Fire in the Valley: The Making of the Personal Computer. New York, NY: McGraw-Hill. p. 329. ISBN 0-07-135892-7. "They brought in Tim Paterson of Seattle Computer Products, located across Lake Washington, to try to build a card for the Apple that would let it run Microsoft's 8080 and Z80 software. They called it the SoftCard. Paterson did a series of prototypes before Don Burdis took over the project."
- "Z-80 Board Puts CP/M on Apple". Infoworld (Popular Computing) 2 (6): p. 3. April 28, 1980. ISSN 0199-6649.
- "Seminar Spills Negotiating Secrets". Infoworld (Popular Computing) 2 (21): p. 24. November 24, 1980. ISSN 0199-6649. "Unsure of the demand for the product, Microsoft took a prototype to the last West Coast Computer Faire"
- Ballmer, Steve. "Microsoft Surface Keynote". Retrieved 19 June 2012.
- Pelczarski, Mark (November 1981). "Microsoft Softcard". BYTE. pp. 152–162. Retrieved 19 October 2013.
- AppleLogic website, showing peripheral cards for the Apple II series of computers, including the Microsoft Softcard