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Path: utzoo!utgpu!watmath!uunet!xanth!mcnc!gatech!rutgers!mit-eddie!andante!ulysses!att!icus!lenny
From: lenny@icus.islp.ny.us (Lenny Tropiano)
Newsgroups: unix-pc.general,comp.sys.att
Subject: Re: Second Hard Drive for UNIX-pc; HwNote10
Summary: Why the need for P5.1...
Message-ID: <563@icus.islp.ny.us>
Date: 3 Jan 89 19:37:31 GMT
References: <413@limbic.UUCP> <450@uncle.UUCP> <417@limbic.UUCP> <10@taqwa.UUCP> <7348@chinet.chi.il.us> <420@limbic.UUCP>
Reply-To: lenny@icus.islp.ny.us (Lenny Tropiano)
Distribution: unix-pc
Organization: ICUS Software Systems, Islip, New York
Lines: 31

In article <420@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes:
...
|>
|>Furthermore, it means that you have to consider which upgrade will provide
|>the bit for P5.1.  Then you will end up having to install both if you
|>want to use the upgrade that doesn't do P5.1.  I believe you need P5.1
|>in order to use the second hard disk select bit.
|>
...
This is absolutely true.  The kernel checks for the revision level of
the motherboard at location  "revlev".  If your board doesn't show that
it's a P5.1 board, then the code for the 2nd drive will never be executed.
John Milton did some work early on by fooling the kernel into thinking
it's running on a P5.1 board, by writing the correct value into "revlev"
using the old "adb /unix /dev/kmem" method.  This had some strange side 
effects if I remember correctly? (John, what have you found?)  

As Gil said, the P5.1 circuitry is minimal, and it does give the possibility
of installing *large* hard drives in your system, provided you have the
proper power supply to run them.  You don't have to, but it does allow you. 
Just think, two Maxtor XT2190 (159MB) drives ... Hmmm... :-)   Most importantly
it saves opening the machine to do the upgrade for P5.1/4-head select down
the road :-) ...

... Hungry for more space,
Lenny
-- 
Lenny Tropiano             ICUS Software Systems         [w] +1 (516) 582-5525
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