SMD disk specifications

Eric Smith spacewar at
Fri Dec 13 13:35:47 CST 2019

On Fri, Dec 13, 2019 at 11:10 AM Al Kossow via cctalk <cctalk at>

> ANSI has a spec, X3.91M_1987 I don't know if it covers the SMD-E , etc.

X3.91M-1987 section 6 covers "Interface Extensions", which includes adding
tag 4, 5, and 6, dual-port provisions, spinup sequencing, index mark and
sector mark signals, fixed-head addressing, service voltages on round
radial cable, and extended cylinder addressing. I think some of that came
in with SMD-E, but I'm not 100% certain. X3.91M-1987 describes data rates
of up to 24 Mbps, which came from SMD-E.

SMD-E is apparently defined by CDC document 64712402, which I've never been
able to obtain.

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