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Path: utzoo!watmath!clyde!burl!mgnetp!ihnp4!zehntel!dual!amd!decwrl!decvax!mcnc!ecsvax!mjg
From: mjg@ecsvax.UUCP
Newsgroups: net.micro.pc
Subject: Re: re: unerase
Message-ID: <2967@ecsvax.UUCP>
Date: Fri, 20-Jul-84 10:46:00 EDT
Article-I.D.: ecsvax.2967
Posted: Fri Jul 20 10:46:00 1984
Date-Received: Fri, 27-Jul-84 06:10:21 EDT
References: microsof.8700
Lines: 19


To a limited extent you can recover a file if you have accidentally erased
it providing you have not written anything else to the disk in the mean
time. Erasing the file causes the first byte of the name to be zapped with
a character (usually an E5 hex) which causes DOS to think it is not there.
The directory entry contains a pointer to the 1st cluster of the file and
to the entry in the FAT table which points to the next cluster which in
turn points to the next cluster and so on. Now these entries are erased
from the FAT table when you erase the file so on the face of it you only
have information on the first cluster. HOWEVER, DOS normally allocates
free clusters on a basis of taking the next free cluster starting from
the lowest numbered one available. Therefore it is possible, knowing
the length of the file and the first cluster to reconstruct the entire
file.

As I said, this is only if you have not written a new file to the disk
since last time. If you have then all bets are off.

Mike Gingell      ...decvax!mcnc!ecsvax!mjg