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From: mjg@ecsvax.UUCP (Michael Gingell)
Newsgroups: comp.sys.ibm.pc
Subject: Re: 720k on a standard disk? (comment)
Message-ID: <3651@ecsvax.UUCP>
Date: Wed, 5-Aug-87 10:26:53 EDT
Article-I.D.: ecsvax.3651
Posted: Wed Aug  5 10:26:53 1987
Date-Received: Sat, 8-Aug-87 01:33:16 EDT
References: <1802@bellcore.bellcore.com> <1842@nicmad.UUCP>
Distribution: na
Organization: UNC Educational Computing Service
Lines: 22
Summary: yes it is possible




It is possible to make a 1.2 meg drive write 720 k on standard
disks. A 1.2 Meg drive is 80 track double sided and is normally
controlled by your AT's BIOS to write in high density 80 track
(1.2 Meg mode) or in low density 40 track (360K) mode. In 360k
mode the drive double steps. To get 720k in low density you
have to have an additional software driver that does more or less
the same code as for 360k except that the double stepping is
eliminated and a new disk parameter block specifying this format
must be selected while accessing this format.

To do all the above you have to have a software driver resident in
RAM which intercepts the Disk I/O INT 13H or 40H and checks to see
]if this is a 720k request for a sector read write or format, if so
it must handle the call itself else pass it to the regular BIOS
handler.

Any volunteers to write the code for this ?

Mike Gingell    ....decvax!mcnc!ecsvax!mjg