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Date:      Sun, 05 Mar 2000 09:49:01 +0100
From:      sthaug@nethelp.no
To:        kc5vdj@swbell.net, jbryant@ppp-207-193-2-159.kscymo.swbell.net
Cc:        mbac@nyct.net, freebsd-hackers@FreeBSD.ORG
Subject:   Re: Copy-on-write filesystem
Message-ID:  <57769.952246141@verdi.nethelp.no>
In-Reply-To: Your message of "Fri, 03 Mar 2000 20:45:18 -0600 (CST)"
References:  <200003040245.UAA10031@ppp-207-193-2-159.kscymo.swbell.net>

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> > Imagine: cp file file2, file and file2 reference the same exact blocks,
> > but modified chunks of file2 would be given their own private blocks.
> 
> This is not a microsoft innovation, actually, I believe it was a VMS
> innovation.  It's called a generational filesystem.  the original is
> stored, and later generations of the file are stored as diffs.

As far as I know, VMS simply stores whole files - no diffs involved. Now
if you go back to for instance Univac 1100 and the Exec-8 OS (I suppose
it is OS-1100 now), you'll find a system that *did* store the diffs. In
the form of punched card images! :-)

Steinar Haug, Nethelp consulting, sthaug@nethelp.no


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