Date   : Mon, 27 Sep 1982 19:10:22 EST (Monday)
From   : Mike Meyer <mwm@Okc-Unix>
Subject: Re: Argh..#@&%^% CP/M

Having a sector somewhere on track 0 that told you usefull information
about the disk would be nice. Unfortunately, it wouldn't give the
"infinite portability" you seem to want. Problems show up in figuring
out what format track zero is in to begin with, and then as to whether
or not your hardware will read said disk. For example, I recently got a
standard 8" disk from a friend - I couldn't read it. Seems that there
had been a third party (going from my S100 8" to friends Apple 5 1/4")
who had copied the stuff to a double sided diskette, in standard 8" single
density format. My system doesn't recognize that a double density diskette
is something it can read. Tack onto this the fact that not everybody uses
the WD 177x controllers (for instance, I have an NEC PD765) and there
are formats that some chips will write that others won't read...

A couple of us localy have considered putting in a "mount table" for
a fifth (or third) disk. Said disk would have no entries for the translate
table or DPB (I think I grabbed the right block). When the user issued
a "mount cromdb26 b:", the system would dig those tables up out of a disk
file, and patch them into the  bios. At the same time, the disk B DPH would
be fixed to use the tables. This may be similar to your login command, but
was designed specifically to let us read ANYBODIES diskette (withen
aforementioned chip limitations). The problem is that this thing is VERY
dangerous (at the same level as multiple density 1.x systems), VERY system
dependent, and would require much work to add a new disk format. We eventually
decided that it wasn't worth the trouble - the two of us could share 8"
SSDD, and
8"SSSD worked reasonably well for everybody else.

       mike