On Fri, 6 May 2005, Ethan Dicks wrote:
SMD drives were uncommon for PC-class hardware, but
were quite common
for minicomputers, especially in the PDP-11 and VAX worlds where
people didn't want to pay DEC's prices for DEC's disks.
I ran two different SMD drives and two different SMD controllers
in the S100 world, both CP/M-80 and PDOS. 1979 - 1982 or so.
Both the Konan two-board controller and some clever thing with a
serial hardware state machine, single board. I could look it up, I
still have the source to the driver printed out. Name had an X in
it.
Drives were some rack mount boat-anchor Fujitsu monstrosity (14"?)
that never really worked right, and a BASF 6172 (8", voicecoil, 3
heads) spectaculary fast and spectacularly unreliable POS. The 4th
surface was servo, it would get lost, the drive would go
"wooooOOOOOP KLUNK" and you had to power it down and restart. Ugh.
I always pictured the problem as the track register wrappign
around and seeking to track fffffff instead of 0. Man I spent a
lot of time on that drive with a scope.
The x-named controller had some internal statemachine that you had
to squirt microcode to; the microcode was provided as a printed
table of bytes, unique to the drive, and provided by the
manufacturer. If I recall the interface was peculiar but it
worked. Programmed IO (INIR, Z80) I think; less performance, but
reliable.
The Konan was DMA, and you had to adjust buss timing on the CPU,
memory, and Konan and it wasn't really possible to get all three
reliably compatible all the time. That Konan controller had more
jumpers than any other computer board I ever used!