24 Sep
2019
24 Sep
'19
4:13 p.m.
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.