Raymond Check discusses MS DOS Floppy Disk Cache
cisin at xenosoft.com
Tue Sep 24 18:13:27 CDT 2019
On Tue, 24 Sep 2019, Chuck Guzis via cctalk wrote:
> I don't quite get the bit about the NAND gate, but back in the days of
> 5.25" floppies there was a way around that one.
> One need only monitor the drive write-protect status every tick or so.
> If it toggles, invalidate the cache.
> I implemented it on a 8085 system, checking the write protect status
> every 250 msec. The drive needn't be spinning. If you insert or remove
> a 5.25" disk, the status will change.
> We even went a bit further and checked to see if the disk contained any
> files open for writing. If so, we sounded an alert and froze the system
> until the subject disk was re-inserted. This reduced the number of
> disk-swapping related errors essentially to zero.
And, it presumably worked just fine.
They tried TWO of their staff, and neither could change a disk in less
that 2 seconds.
COULD somebody go from write protected 8" or non-write-protected 5.25"
(did you sense door open?) to disk out of drive in under 250ms, and then
lso go from door open, no disk to non-write protected disk in drive (door
still open?) in under another 250ms? I can't. But if somebody
could, then you just need to change that user's settings to about 100ms.
More information about the cctech