Date: Fri, 8 Sep 1995 19:17:08 +1000 From: Bruce Evans <bde@zeta.org.au> To: freebsd-hackers@freefall.freebsd.org, msmith@atrad.adelaide.edu.au Subject: Re: higher density diskettes Message-ID: <199509080917.TAA08205@godzilla.zeta.org.au>
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>> I bet the root directory and the single file therein are actually >> dummies. They are only there to not confuse people looking at it >> without the proper driver loaded. >I'd daresay they are - I'd guess that the FAT is only 1 sector long, >and various other space-saving things too. >> I've already been discussing this with Bruce (altough, this has been >> at the time the article about OS/2's install floppies appeared here), >> and the result was that it's rather useless since the BIOS cannot >> handle it, and our installation procedure does require a single (1.2 >> MB !!!) floppy at all. IIRC the DMF has sectors of various sizes on each track. There's at least one 512-byte sector. This could be used for the boot sector to keep boot loaders happy. The FAT and directory could be placed on other 512-byte sectors so that they can be read by dumb drivers. Then "DIR" could work with no special support, at least if the floppy isn't cached. >Does the BIOS actually rangecheck the sector numbers you try to read? >Talk about a nuisance 8( (As suggestions go, it wasn't a bad one) I think some do. An old bug report and/or comments in the Linux loader say that some SCSI BIOSes screw up the floppy parameter table, leaving it with 9 sectors, and then attempts to read sectors > 9 fail. The fix is to write a suitably large number to the sectors field of the parameter table. The parameter table is used mostly for formatting and it apparently doesn't hurt to have a larger than necessary number there for anything else. Many floppy drivers are challenged by variable sized sectors :-). They should probably use a track buffer and present only 512-byte sectors to the OS. This would be a lot of work for a small gain in space and a loss of time. Bruce
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