🚀 go-pugleaf

Landon Dyer writes:
> Mediach() on floppies does not simply "check a bit somewhere".  It
> hits the disk (to check the serial number) only as a last resort,
> since ANY disk I/O --- floppy OR hard disk --- is expensive.  I
> suggest you send a packet only as a last resort.

Unless there have been substantial changes to the Bios since the
developer's kit was produced, this is not strictly accurate.
Mediach() NEVER hits the disk, it only computes and returns a mode:
0-safe, 1-unsure, 2-changed.  Rwabs() calls Mediach() and hits the
disk if 1 is returned, changing the mode to 0 or 2 depending on
whether the serial numbers match.  If mode=2, Rwabs does not perform
the I/O but instead returns the media change error (-14).  Getbpb()
resets the mode back to 0.  Mediach() changes the mode from 0 to
1 if a short time (1-2 seconds) has elapsed with no disk I/O and
the write protect bit has been seen on during that time.  The write
protect bit goes on whenever a disk is removed from the drive or
the disk is write protected.

--Mike Fischer <fischer@yale.arpa>
-------