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From: DSullivan.CSC_SDO%hi-multics@sri-unix.UUCP
Newsgroups: net.micro.cpm
Subject: How to mangle a disk.
Message-ID: <15750@sri-arpa.UUCP>
Date: Thu, 19-Jan-84 21:20:00 EST
Article-I.D.: sri-arpa.15750
Posted: Thu Jan 19 21:20:00 1984
Date-Received: Sat, 21-Jan-84 09:04:41 EST
Lines: 19

It doesn't matter if you use reset all drives (function 13) or reset
drive (function 37) the following will muck up files/directories etc
given enough disk requests.
 Step 1) open a file on drive X
 Step 2) open file2 on drive X
 Step 3) write data to file x (less than 16k)
 Step 4) reset the disk. Both function 13 or 37 will do the trick.
 Step 5) write data to file2, the data will be written over file1's
        allocated area.
 Step 6) close the files, and make the damage perminant.
 What happens is the FCB for file1 is given blocks from the free pool
(as kept by the allocation vector)  The reset causes the vetor to be
re-initialized to the old pattern.  The writes to file2 then use the
re-initialized map, and re-allocate to the same space as file1.  These
two files now share a common set of blocks on the disk. Read/write
either and it will impact the data of the other.
 Please note when you have a hard disk, even less checking is done, so
it is easier to mangle the disk esp with BIOS that have disk cashes that
keep parts of directories around.