On Tue, 12 Dec 2000 02:49:59 -0500 (EST), Thomas Mueller asked:
> How much data capacity did those 8" FDs have?
> one. I suppose if an 8" FD drive goes bad, the user is out of luck trying to
> repair or replace it. Besides, the FDs may be past their shelf life (?)
>
241 kilobytes, as I remember, but that might have been after some
space had been taken for the directory. Some odd number of tracks
like 77, I think, and 128 bytes per sector. Possibly 26 sectors per
track. (Sorry for the vagueness - it's a very long time ago!!) You had
to go some to fill a disk up in those days, too! My system only used 126
bytes per sector for data. The last two gave the 16-bit address of the
next sector in the file. Bad news if you got a cobbled sector early on
in a file that you wanted to rescue.
I think that the format had a name like IBM3740 or something like
that. My drives were made by a firm called Calcomp and they were built
like something to be proud of. The earlier drives used all RTL (or was
it DTL?) chips but the later ones had a custom 40-pin IC, which cut
down the area of the PCB somewhat. So at least the earlier ones could
always be repaired.
A 'computer supplies' outfit called Inmac which was around
at the time released a type of disk known as a 'flippy'. This had two
access holes in the sleeve for the 'offset' index hole to see through
so that the disk would work in the single-sided drives either way up
- effectively doubling the amount of storage on a single-sided drive.
Control of the drives by the CPU was by a Western Digital chip called
the 1771, which I seem to remember costing an arm and a leg
(relatively).
Ah - memories, memories....
Ron.
