Path: utzoo!attcan!uunet!portal!atari!apratt
From: apratt@atari.UUCP (Allan Pratt)
Newsgroups: comp.sys.atari.st
Subject: Re: PC compatible(?) format on the ST
Message-ID: <1154@atari.UUCP>
Date: 2 Sep 88 18:07:20 GMT
References: <3461@druhi.ATT.COM> <8662@cup.portal.com>
Reply-To: apratt@atari.UUCP (Allan Pratt)
Organization: Atari (US) Corporation, Sunnyvale, California
Lines: 31

In article <8662@cup.portal.com> Thomas_E_Zerucha@cup.portal.com writes:
> [Media byte, etc.]
>
> But while I am at it, does the BIOS now support any sector size other than
> 512 bytes?  Any other cluster size besides 2 sectors/cluster?  All the other
> stuff in the Bios Parameter Block and Boot sector that are supposed to set
> up all these values?

Thank you for backing me up on the Media Descriptor versus the longhand
information in the boot sector.

We could have used the media descriptor byte F8, forcing the PC driver
to look at the boot-sector information, but those same dumb BIOSes
would make the faulty assumption that the media was nonremovable.
IBM realized the limitations of the media descriptor byte as shorthand
for the rest of the boot-sector information, and, at least in DOS 3.3,
they rescinded it.  Perhaps they did sooner than that; I can't lay my
hands on a DOS 2.x tech ref manual.

A driver can be written to support >512 byte sectors, and I have been
told that GEMDOS will work, but you have to create GEMDOS buffers that
are appropriately sized.  The built-in buffers are 512 bytes, and while
everything else is parameterized to the BPB, that size is fixed.  If you
patch in your own buffers (using the system variable _bufl) it will
work, I have been told.  I have not verified this.  The person who told
me so had old ROMs, so that's even more encouraging.  He said he wrote
a RAMdisk with an Rwabs that returned 1K sectors, and it worked fine.

============================================
Opinions expressed above do not necessarily	-- Allan Pratt, Atari Corp.
reflect those of Atari Corp. or anyone else.	  ...ames!atari!apratt