Back in 1980 — before the release of MS-DOS… and long before the release of Microsoft Windows — the biggest seller for Microsoft was, believe it or not, an add-on card for the Apple II computer which allowed the Apple II to run the CP/M operating system from Digital Research.

The Microsoft SoftCard added a Z-80 CPU to the Apple II, and included some additional CP/M software (including Microsoft BASIC).

While Microsoft was initially uncertain of the market viability of the SoftCard, it turned into their biggest selling product of 1980 — moving over 5,000 units (priced between $349 and $399) in just the first three months.

From November, 1980 Infoworld:

“Unsure of the demand for the product, Microsoft took a prototype to the last West Coast Computer Faire. Unprepared to take orders for the then-unannounced product, Rayburn [who was then the President of Microsoft’s Consumer Products Division] collected over 1000 business cards from interested buyers the first day.”

Sales were good. Reviews were good. The Microsoft SoftCard (powered by Digital Research’s CP/M) was a hit.

From there the SoftCard would become so common that many software packages were shipped specifically for CP/M running on the Apple II. With Microsoft, themselves, shipping additional compilers for the SoftCard-equipped Apple II — including Cobol and Fortran.

Fun Historical Tidbit: Because (at least in part) of the CP/M powered Microsoft SoftCard… IBM approached Bill Gates and company regarding licensing CP/M to run on the new IBM PC. This (after negotiations with CP/M creator, Digital Research, broke down) resulted in an agreement between IBM and Microsoft — just a few short months after the introduction of the SoftCard — where IBM would license a CP/M clone from Microsoft (which Microsoft purchased from a company in Seattle). Cutting Digital Research out entirely. Thus the legacy of MS-DOS was born.  Thanks, in large part, to a CP/M Z-80 card for the Apple II.

Here’s a few extra resources on the Microsoft SoftCard for those interested in this fascinating system. Thanks to the popularity of the SoftCard in the early 1980s, there is a wealth of documentation available (including scans of original documentation such as those included below).