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From: broman@cod.UUCP (Vincent P. Broman)
Newsgroups: comp.os.minix,comp.sys.ibm.pc
Subject: 400K floppy disks
Message-ID: <860@cod.UUCP>
Date: Tue, 13-Oct-87 13:47:58 EDT
Article-I.D.: cod.860
Posted: Tue Oct 13 13:47:58 1987
Date-Received: Thu, 15-Oct-87 05:27:28 EDT
Organization: Naval Ocean Systems Center, San Diego
Lines: 19
Keywords: nonstandard BIOS format floppy disks
Xref: mnetor comp.os.minix:1884 comp.sys.ibm.pc:9022

Does anyone know how to format floppies to a size of 400K?

I know it was done under some P-system (not Pecan) which did not depend on
MS-DOS.  I suppose that one formats 10 sectors on a track instead of the
standard 8 or 9, (though I wonder whether 5 doubly long sectors could have
been used instead).  The ROM BIOS supplies an interrupt service for formatting
various sector sizes and numbers, but it seems to depend on a mysterious
disk parameter table with abstruse entries for intersector gaps and other
arcana not documented.

Supporting "bigger" floppies with standard hardware would be very natural
for Minix to attempt.  Once you are able to format the disks, it should
be straightforward to alter the floppy driver to read and write it.
The main difficulty I see is in simultaneously supporting 360K and 400K
floppies with the same driver.  Perhaps the file system's size field is
just the thing to differentiate between the two varieties at runtime.

Vincent Broman,  code 632, Naval Ocean Systems Center, San Diego, CA 92152, USA
Phone: +1 619 225 2365    Internet: broman@nosc.mil   Uucp: sdcsvax!nosc!broman