GRUPP@mit-mc@sri-unix.UUCP (07/17/83)
From: Paul R. Grupp <GRUPP@mit-mc>
The BIOS supplied with my Morrow M20 hard disk had a bug in the DPB.
This BIOS has equates for the M10, M20, and M26 so if you have one
of these drives with supplied BIOS, you might want to check.
PROBLEM; The DPB reserves 512 directory entries, but the AL0 and AL1
reserve space for 4 time that. This means that there is
48K of unuseable disk space.
TO FIX; Edit the BIOS file equates for your drive (2 DPB's for M10
3 DPB's for M20 and M26) and change the DRM and or AL0 & AL1.
I chose to make 1024 directory entries (as I was running out
of dir space before disk space). To do this set DRM=1023,
AL0=0FFH, and AL1=0 (check that the block size is 4K (BSH=5)
or else these values will have to be changed as per the D.R.
manual). Then assemble the file and use DDT to overlay the
hex file on your sysgen immage, and save.
IF YOU CAN'T fix this yourself (best NOT to try if you don't know) don't
worry... The bug has no effect on the operation of the system other than
waisting some disk space.
--Paul
P.S. The FIX I described will give you 1024 directory entries and 32K
more file space, and will NOT disturb ant pre-existing files or
directory entries.