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From: psfales@ihlpe.ATT.COM (Pete Fales)
Newsgroups: comp.sys.ibm.pc
Subject: Re: Reading Hard disk with different DOS versions
Message-ID: <1969@ihlpe.ATT.COM>
Date: Fri, 21-Aug-87 09:58:19 EDT
Article-I.D.: ihlpe.1969
Posted: Fri Aug 21 09:58:19 1987
Date-Received: Sun, 23-Aug-87 01:35:54 EDT
References: <680@cblpf.ATT.COM>
Distribution: na
Organization: AT&T Bell Laboratories - Naperville, Illinois
Lines: 34


 In article <680@cblpf.ATT.COM>, jpw@cblpf.ATT.COM (Mike Vehonsky) writes:
 > 
 >	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.

I am not positive, but I'll take some guesses:

Guess #1:
It is a well known fact
that Microsoft introduced the 16 bit FAT (i.e. smaller hard disk cluster
size) in version 3.1 (or 3.0??), but AT&T did not introduce it until 3.2.  
This means that once the disk has been formatted with anyone's 3.2, it can 
be read by anyone's 3.2 but only by the Microsoft version of 3.1.

Guess #2 (more likely as I think about it):
If the disk on your second system was formatted with pre-3.2 and then
3.2 installed without reformatting, it will retain the larger cluster
size.  Thus, it can be read by any version of DOS.

-- 
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