Most Z80-based Amstrads (CPC664. CPC6128, PCW8256,
Spectrum +3) along
with the Tatung Einstein and Oric used a 3" drive. I've seen this drive
sold as an add-on for things like the BBC micro
I saw an ad in an Apple ][ magazine that advertised one for the Apple ][.
There were regular ads in Hot CoCo and Rainbow magazines for these as well
-- a little expensive, but they were advertised as 'flippy' disks straight
off, so the amount of storage was rather good for the time...
Hitachi made single and double head 40 cylinder drives that had a
stnadard SA400-like interface connector. The single-head was a flippy,
the double-head one wasn't (and since the spindle motor didn't reverse
when you selected the second head, it couldn't read the 'flip side' of a
disk from the single-head drive).
When it was clear that the 3" disk was not going to catch on (a pity,
since it's mechanically superior to the 3,5" one), the drives were sold
off in the UK fairly cheaply. I added one to my CoCo system...
Amstrad machines used a drive with a 26 pin (IIRC) connector, much the
same signals as the normal SA400 interface, but a different
connector/pinout. They used either a single-head 40 cylinder drive or a
double-head 80 cylinder one. At one point in the UK, disks were labelled
for 'single head' or 'double head' drives, when what they actually meant
was 40 or 80 cylinder. Since the single-head drive was a flippy, _all_
the disks were tested (and good) on both surfaces.
Amusing-ish story. I needed a blank disk for the drive in my CoCo, and I
went to a local shop to buy one (or more). The salesdroidess said 'We
don't have any 3" disks. We've got 3.5", can you cut them down?'.
She
then offered me 3" disks at the 3.5" price (which was considerably
less)... Go figure...
-tony
