From: NoEmailAds AT execpc DOT com (Chris Giese)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: 18-sector limit with biosdisk()
Date: Tue, 13 Feb 2001 02:04:04 GMT
Organization: PROPULSION GROUP
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To: djgpp AT delorie DOT com
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Jason Green <news AT jgreen4 DOT fsnet DOT co DOT uk> wrote:

>DJ Delorie <dj AT delorie DOT com> wrote:
>
>> > Could this limit be removed in the next version of the C library?
>> > Or raised to 21 sectors? The Win95 install floppies have
>> > 21 sectors per track (1.68 meg per disk), as do various
>> > demo disks, OS boot disks, etc.
>> 
>> It can be raised pretty easily, but making it dynamically adjust will
>> be trickier.
>
>> Does anyone know of any floppies with more than 21 sectors that the
>> BIOS calls support?

Linux bootsect.S mentions "2.88 ED" disks with 36 sectors per track,
but I've never seen such a disk.

I once tinkered with superformat and fdformat, trying to make my
own Linux boot/root disk. In my limited experience, floppies with
more than 21 sectors per track range from impossible to unreliable.

>Here is a reply I received from tom AT toms DOT net in relation to booting
>Linux from an oversize floppy, it might have some relevance here.  
>
>> Well, many bioses will not boot with the 'compact' option, because they
>> don't know how to deal with a full-track 21-sector read.  They can read
>> one sector at a time up to track 21, but if you say, 'read 21 tracks to
>> the buffer starting at track 0', they choke.  So, with LILO you have to

I have experimenting with boot sectors lately, and I wonder if
it's REALLY the BIOS that makes oversized floppies fail. Maybe a
bootloader fails to patch the maximum sectors-per-track value in
the floppy parameter table (FPT). Or maybe it makes a bad guess
or assumption about the floppy geometry.

Last time I checked, the built-in loader of Linux (bootsect.S) patches
the FPT, but does NOT support 21 sectors per track. I downloaded Tom's
boot/root disk, and it worked OK. His disk has 21 sectors per track,
82 tracks, and boots with LILO.

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