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From: jso@edison.UUCP (John Owens)
Newsgroups: net.micro.pc
Subject: Re: Re: IBM PC/XT UPGRADE
Message-ID: <759@edison.UUCP>
Date: Wed, 4-Jun-86 16:47:47 EDT
Article-I.D.: edison.759
Posted: Wed Jun  4 16:47:47 1986
Date-Received: Sun, 8-Jun-86 06:03:54 EDT
References: <846@mhuxt.UUCP> <692@nicmad.UUCP> <4948@ut-sally.UUCP> <704@nicmad.UUCP>
Organization: General Electric Company, Charlottesville, VA
Lines: 45

> In article <4948@ut-sally.UUCP> nather@ut-sally.UUCP (Ed Nather) writes:
> >Not so.  We run 20 MB disks under DOS 2.1 with no problems, other than
> >those caused by the 12-bit FAT pointer which limits the minimum size of a
> >file to 8K bytes.
> 
> I have to disagree.  I quote the following from the PC-DOS 3.10 Tech Ref Man:
> 
> 	The FAT consists of a 12-bit entry (1.5 bytes) for each
> 	cluster on the disk or a 16-bit entry (2 bytes) when a
> 	fixed disk has more than 20740 sectors as in the case
> 	for fixed disks larger than 10M bytes.
> 
> Also:
> 
> 	16-bit FATs are for use with DOS versions 3.00 and 3.10.
> 
> The only way you can have PC-DOS 2.10 run 20MB hard drives is if:
> 	1. You run partitioned drives with two 10MB partitions or
> 	2. You butchered the drive to fool DOS
> As PC-DOS 2.10 stands, it is not able to format 20MB hard drives as 20MB.
> 
> So, in conclusion, the original poster still needs PC-DOS 3.10 or 3.20.
> 
> Mr. Video      seismo!uwvax!nicmad!brown

Sorry, he can still run 2.1.  I know; I've done it.  (I've also
written a driver to allow using two partitions, but anyway....)

What you've demonstrated with your quotes is exactly what he was
saying originally; with DOS 3.0 or greater, he can use 16 bit FATs,
allowing him a much smaller minimum file size, and therefore more
efficient allocation.  With DOS 2.1, he can only have a 12-bit FAT,
therefore he can only have up to 4096-10=4086 clusters, therefore,
with a 20MB disk, his cluster size is 16 sectors, or 8K.  (The cluster
size must be a power of 2.)

You still get 20MB of disk space, but it's not allocated very well,
and you'll end up using most of your space for what would take less
under 3.10 (unless you consistently have *very* large files.)

	John Owens @ General Electric Company	(+1 804 978 5726)
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