On 3 Jan 2010 at 17:46, Tony Duell wrote:
As an aside, I have a machine using standed
'360K' 5.25" drives --
that is Tandon TM100s -- which does correclty implent a disk-changed
feature. How it does it is to have the 2 drives separately cabled to
the controller board and the drives always selected. It then looks for
a change-of-state of the write-protect line. This must change if a
disk is inserted or removed.
Anyone want to guess the machine? I have 3 of them, all different
models (one only has on disk drive).
Heh, nihil sub sole novum.
I implemented that on the Durango F85 in 1979, but I don't think
that's the machine you mean. We had a terrible problem with
customers simply changing diskettes whenever they wanted. The drives
were cabled normally, just selected and the status of the write-
protect line checked every few hundred milliseconds. The FDC was a
WD1781, so WP status was available all of the time, regardless of the
state of the motor. The drives were TM-1004Ms or Micropolis 1610s.
If a change in WP status was detected, the open file table was
checked. If a floppy had files open only for reading, a flag was
set, instructing the OS (not CP/M) to re-read the directory. If a
floppy contained drives open for writing, the system locked out any
operator action until the floppy was reinserted--and displayed a
flashing message on the screen and a repeating beep. Very annoying,
but very effective.
Many drive vendors offered a door-lock feature, but that could get to
be annoying should the OS have a problem.
One problem we never did solve was that of the customer powering the
machine down, without exiting an application. But that persisted on
all systems until someone invented the "soft power" button.
--Chuck