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From: gmv@cblpf.ATT.COM (G. Michael Vrbanac)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Reading Hard disk with different DOS versions
Message-ID: <683@cblpf.ATT.COM>
Date: Thu, 20-Aug-87 13:34:33 EDT
Article-I.D.: cblpf.683
Posted: Thu Aug 20 13:34:33 1987
Date-Received: Sat, 22-Aug-87 12:15:35 EDT
References: <680@cblpf.ATT.COM>
Distribution: na
Organization: AT&T Bell Laboratories - Columbus, Ohio
Lines: 29

> 	If a hard disk has been formatted with DOS version "X",
> 	what determines whether or not you will be able to read
> 	it when you boot DOS version "Y" from floppy.
> 
> 	We just loaded 3.2 on our system (PC6300, 10 Meg).  If
> 	you boot version 2.11 or 3.1 from floppy, and try to
> 	access the C: drive, you get an "Invalid drive specification".
> 	I think that it may have to do with cluster size, but the strange
> 	thing is that another machine (also running 3.2) CAN be
> 	booted with a different version and read the hard drive just
> 	fine.  Any insight would be appreciated.
> 
> 						Mike Vehonsky
> 						ihnp4!cblpf!jpw

To draw an analogy to the UNIX world, the DOS format really doesn't "format"
but rather makes a file system. (a PC "low-level" format is equivalent to
a UNIX "format").  The DOS "file-system" changed with version 3, and is
downward compatible with DOS 2.xx but not upward compatible with DOS 2.xx.

Thus a machine booted with 3.2 can read 2.xx disks, but a 2.xx DOS can't
read 3.2 formatted disks.

Note this is the 12-bit versus 16-bit FAT (file-allocation-table) change.

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 | Mike Vrbanac   AT&T Bell Laboratories   Columbus, Ahiya |
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