Date: Fri, 8 Sep 1995 19:18:34 +0930 (CST) From: Michael Smith <msmith@atrad.adelaide.edu.au> To: bde@zeta.org.au (Bruce Evans) Cc: freebsd-hackers@freefall.freebsd.org, msmith@atrad.adelaide.edu.au Subject: Re: higher density diskettes Message-ID: <199509080948.TAA01450@genesis.atrad.adelaide.edu.au> In-Reply-To: <199509080917.TAA08205@godzilla.zeta.org.au> from "Bruce Evans" at Sep 8, 95 07:17:08 pm
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Bruce Evans stands accused of saying: > 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 That's extremely rude, and not likely to be of much use to us (unless someone writes a modified fdc driver for booting purposes. That's not my hand up, I only know the 1772 8) > >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 That's a job for the bootsector code to deal with. It would be _risky_, but the Atari world went through all this years ago (I expect that the Amigans did a similar thing). The upshot was that 10 sectors a track on 720, and 20 on 1440 disks was close to 100% reliable. Lots of people used 11/22 sector formats with minimal grief. > 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. That sounds like an implicit 'it might work' 8) But there still needs to be something to format and write the disk in the first place. Not fun, perhaps. > Many floppy drivers are challenged by variable sized sectors :-). I can't say I'm suprised 8) > 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. Can the 765 read 'raw' tracks, as well as pick sectors out of them? > Bruce -- ]] Mike Smith, Software Engineer msmith@atrad.adelaide.edu.au [[ ]] Genesis Software genesis@atrad.adelaide.edu.au [[ ]] High-speed data acquisition and [[ ]] realtime instrument control (ph/fax) +61-8-267-3039 [[ ]] My car has "demand start" -Terry Lambert UNIX: live FreeBSD or die! [[
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