1581 bug

From: William Levak <wlevak_at_SDF.ORG>
Date: Tue, 27 May 2014 11:47:11 +0000 (UTC)
Message-ID: <Pine.NEB.4.64.1405271134460.23299@sdf.lonestar.org>
I got a read error on my 1581. I got out my disk utilities to see if I 
could read the bad sector.  I found part of the directory on the bad 
sector. With further manipulation of the disk, I found different data on 
the bad sector.  The disk was write protected, and I did not write any 
data.

Then I remembered that the 1581 has a full track buffer.  When you read 
from the disk, it reads a full track into the buffer and sends data from 
the buffer, until you read from a different track.  Apparently, when you 
get a read error, it does not write over the previous contents of the 
buffer for the affected sector.  Subsequent reads for that sector do not 
give an error, but give erroneous data.



wlevak@sdf.lonestar.org
SDF Public Access UNIX System - http://sdf.lonestar.org

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Received on 2014-05-27 12:03:31

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