8-Nov-83 15:04:30-MST,1261;000000000000
Mail-From: WANCHO created at  8-Nov-83 15:01:35
Date: 8 Nov 1983  15:01 MST (Tue)
Message-ID: <WANCHO.11966065606.BABYL@SIMTEL20>
From: WANCHO@SIMTEL20
To:   NORTHSTAR-USERS@SIMTEL20
Subject: Unofficial Patch

In the SELDSK routine of the BIOS in both rev 1.1.0 and 1.2.0, there
is some obsolete code that needs to be disabled.  The original intent
of the code was to force a write of the very first sector to a newly
selected disk to determine right away if the disk was not READ-ONLY,
or the door was open, etc.  However, the auto-select feature of BDOS
subverts this and EACH sector is force-written instead of just the
first.

This bug was discovered by Sigi Kluger when he wondered why a new
version of SWEEP took almost FIVE times longer to copy a file to
another drive than the old version did.  The reason was that the new
version did not log the destination drive first, but depended on that
auto-select feature of BDOS.  It was also discovered in beta testing
that new version that only the North Star CP/M exhibited this problem.
The new SWEEP has since been fixed to log the drive first.

The fix to the North Star 1.1.0 and 1.2.0 BIOS is a one-byte patch:

at BIOS+3B7 replace the DCR A (3DH) with a NOP (00H).

--Frank