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From: grege@gold.GVG.TEK.COM (Greg Ebert)
Newsgroups: comp.sys.ibm.pc.hardware
Subject: Re: Making a floppy drive ignore high density hole
Message-ID: <1184@gold.GVG.TEK.COM>
Date: 19 Jul 90 19:41:42 GMT
References: <11547@ingr.com> <1990Jul19.021714.10040@world.std.com> <803@digi.lonestar.org>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 16


I've been tinkering with a 3.5" drive, and although there is a signal which
the drive generates based upon the type of disk (720/1.44M), it seems to be
unconnected (hence ignored) by the floppy controller, as far as I can remember.
Thus, I don't think a toggle switch will solve your problem.

The difference between 720K and 1.44M formatted diskettes is single vs. double
density, and not narrower tracks as in 1.2M floppy drives. All 5.25" drives
are asumed to be double density.

My MSDOS technical information regarding FATs, etc is a bit outdated, but it
does describe single and double-density 8" diskette support. Basically, an
attempt is made to read the disk in single density. If a read-error occurs,
an attempt will be made using double density. I conclude that it is a BIOS
constraint whether your 3.5" drive is 720K or 1.44M. Any BIOS gurus out there
wish to comment ?