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From: keeshu@nikhefk.uucp (Kees Huyser)
Newsgroups: comp.sys.atari.st
Subject: ROM patch for faster disk I/O
Message-ID: <58@nikhefk.UUCP>
Date: Thu, 13-Nov-86 21:46:27 EST
Article-I.D.: nikhefk.58
Posted: Thu Nov 13 21:46:27 1986
Date-Received: Fri, 14-Nov-86 02:02:57 EST
Reply-To: keeshu@nikhefk.uucp (Kees Huyser)
Organization: Nikhef-K CSG
Lines: 43
Apparently-To: rnews@mcvax


I'm posting this for a friend of mine who has no netaccess :


----

Someone asked me about the ROM patch I mentioned in a net posting earlier.
I dug up some information 'bout it.
 
 The ROM patch involves the Atari U7 ROM (U7 relates to the PCB name for that
 ROM, visible when you open the case of your ST. It's located in the lower left
 corner of the PCB).
  
  It appears to be that the ST ROM's double-check the track the diskarm is at,
  whereas the disk-controller already performed that check. So your ST is
  'double-sure' it's on the right track when it performs read or write seeks.

  This, ofcourse, is nonsense. So clever folks somewhere in Germany found a
  way of defeating the double-check. They changed only one bit in the U7
  ROM, which makes it much, much faster. I received my patched ROM without
  having to make any patches myself, but I'm pretty sure the following 
  information is accurate. Just to be on the safe side: I have a 1040 ST 
  with normal, legal ROM's, but I replaced the U7 with a patched EPROM. 
  No hardware modifications are necessary, it's a clean job.
   
Location $0CD7 (that is, ofcourse, hex) holds value $14 (also hex). When
changed into $10 (hex again), the disk I/O becomes a real joy. That's it.
I believe you need a 27256 EPROM to do the job.

					Paul Molenaar

----

Replies to the above posting can be send to me.

					Kees Huyser

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|  Kees Huyser
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