Path: utzoo!mnetor!uunet!seismo!sundc!pitstop!sun!oliveb!pyramid!octopus!pete
From: pete@octopus.UUCP (Pete Holzmann)
Newsgroups: comp.sys.ibm.pc
Subject: Re: big disks on PC AT clones
Message-ID: <207@octopus.UUCP>
Date: 1 May 88 05:10:05 GMT
References: <21346@amdcad.AMD.COM> <205@octopus.UUCP> <1570@pt.cs.cmu.edu>
Reply-To: pete@octopus.UUCP (Pete Holzmann)
Organization: Octopus Enterprises, Cupertino CA
Lines: 28

In article <1570@pt.cs.cmu.edu> ralf@B.GP.CS.CMU.EDU (Ralf Brown) writes:
}In article <205@octopus.UUCP> I write:
}}[Boot partitions often have to be bigger than 16MB or you can't boot from
}} the hard disk. Has to do with FAT table sizes, but why, I don't know].

}The reason is that DOS FORMAT (and likely a lot of other programs) use 12-bit
}FATs for drives <16M, and 16-bit FATs for drives >16M. [explains the pain
}of forcing small clusters/big FAT on partitions <16M]

Thanks for filling out the FAT size explanation. Unfortunately, I still
don't know why the 12 bit fat on small partitions disables booting off the
disk! Does anybody know for sure? I could make a wild guess, which would be:
DOS looks at the DRIVE size, sees that it is big, assumes a big FAT, then
chokes on the small fat actually present in the boot partition. <<<That
was a GUESS, not FACT>>>... obviously DOS is *able* to boot off of small-
FAT drives, else you couldn't have a 10MB boot drive under current DOS
versions...

Does anybody know fer shure?


Pete

-- 
  OOO   __| ___      Peter Holzmann, Octopus Enterprises
 OOOOOOO___/ _______ USPS: 19611 La Mar Court, Cupertino, CA 95014
  OOOOO \___/        UUCP: {hpda,pyramid}!octopus!pete
___| \_____          Phone: 408/996-7746