Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 beta 3/9/83; site microsoft.UUCP
Path: utzoo!linus!decvax!microsoft!markz
From: markz@microsoft.UUCP (Mark Zbikowski)
Newsgroups: net.micro.pc
Subject: Position dependency in FORMAT/DISKCopy
Message-ID: <8678@microsoft.UUCP>
Date: Mon, 9-Jan-84 12:42:00 EST
Article-I.D.: microsof.8678
Posted: Mon Jan  9 12:42:00 1984
Date-Received: Tue, 10-Jan-84 05:47:58 EST
Organization: Microsoft Corporation
Lines: 11

The apparent position sensitive code in FORMAT/DISKCOPY, etc is due to an
unfortunate bug in the IBM ROM.  When performing any disk operation (except
format), register AL has the number of sectors to be transferred.  The ROM
performs a simple check with this number and ES:BX to see if there is a
64K boundary in the range.  If so, it reports a DMA violation.

Unfortunately, the format command to the ROM places the number of sectors to
be formatted in AL and ES:BX points to a table of 4 byte records, one for
each sector to be formatted.  The ROM then uses the SAME test to see if there
is a segment violation.  The test is inappropriate and, in this case, totally
incorrect.