Anyone know where the Step/Direction version of the FDD interface

So far as near as I can tell the earliest FDDs (IBM 23FD Minnow and Memorex
650/651) used Step In/Step Out. The IBM 33FD Igar used direct control of the

The earliest Step/Direction FDD I can find is the Shugart 800 which first
shipped in September 1973.


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