Schauble@MIT-MULTICS.ARPA (01/17/84)
Some disk drives (my Qume DT8's for example) have a "disk change" line on the interface. This is driven by a flip-flop that is set when the door is open and reset when the drive is unselected while ready. If you select the drive and find -ready, there is presently not a disk in it. If you find it ready and disk change, someone changed the disk while you weren't looking. I don't know about the existance of this feature on 5 inch disks. I do know that the IO driver discriptions for MS/DOS document an entry point for "is this disk changed since the last I/O operation" that can return "yes", "no", or "I don't know". So I suspect that it occurs on 5 inch disks also.
korfhage%ucla-ats@sri-unix.UUCP (01/17/84)
From: Willard Korfhage <korfhage@ucla-ats> Floppy disk controller chips can check for an open door by monitoring the sector hole sensor (the 1791 does this). If the chip doesn't receive a pulse from the sensor within xx milliseconds of the last pulse, then it knows the disk has stopped rotating, presumably because the door has been opened. If I read the data sheet properly, the 1791 can send an interrupt when this happens. This technique, of course, works for any floppy, regardless of size. Willard Korfhage
Damouth.Wbst@PARC-MAXC.ARPA (01/18/84)
" . . monitoring the sector hole sensor . . . works for any floppy, regardless of size ." Sorry - not true. You forget that some 5 1/4" drives are soft sectored. The Apple II drives are not only soft sectored, they don't even use the once-per-revolution index hole. /Dave
perl@rdin.UUCP (Robert Perlberg) (02/03/84)
cFb|* Willard Korfhage suggests that the index hole sensor can be used as a drive door sensor since the disk stops spinning when you open the door. This would not work on most 5.25" drives since the disk times out and stops spinning whenever it is not being accessed. (nice try) As a point of interest to this discussion, Hewlett-Packard used to make a machine called the HP250. Although it didn't run CP/M or anything like it, it had a kind of 8" floppy drive I have never seen elsewhere. The drive door could be locked by software so the user could be physically prevented from removing the disk! Also, when you closed the door, you could hear the machine accessing the disk; probably reading the directory. (Note that the HP250 was a multi-tasking multi-user system.) Robert Perlberg Resource Dynamics Inc. New York philabs!rdin!rdin2!perl