Subject: Re: AMD 586 dx4 133 support
To: Jeff Northon <>
From: Michael L. VanLoon -- <>
List: port-i386
Date: 09/11/1996 22:45:27
>> I'm not positive, but the Intel DX4 might have come at the start with
>> a 16KB cache.  If it did, it was write-through originally, and only
>> became write-back on the newer "write-back enhanced" 486DX4s.

>So what is the deal with the write-back and busmaster controllers?
>Could that have been why our intel DX4 100 was dumping core and panicin'
>(Adaptec 1742 EISA), what would have worked, write-through? 
>At least when it panicked it would write out the memory image and .core
>file @48 megs (ouch).

Yes, that's quite possible.  In fact, that would be exactly the
behavior I'd expect to see in such a situation.

If your motherboard didn't know how to
support write-back, but somehow managed to turn it on in the CPU

Normally, the write-back enable pin isn't wired on an older 486
motherboard, so the CPU comes up in write-through mode on those older
boards [like mine].  At least with the AMD CPUs anyway.  Not sure of
if the Intel chips do the same thing.  Newer motherboards that are
designed to support these chips wire that extra bin, and usually give
you an option in the BIOS.  It's possible that even if your
motherboard wasn't designed for it, you could still get a BIOS upgrade
that would let you explicitely control this.

>We put the intel DX2 66 back in and problem went away. Sure miss the 
>speed the DX4 100 had.

It could be the write-back.  It could also be that some timing was
just slightly out of tolerance somewhere.

If you can turn off write-back in your BIOS (your BIOS needs to be
write-back aware -- i. e. has to know about the newer DX4s'
capabilities), then you certainly could try it again with the DX4 and
write-back disabled.

  Michael L. VanLoon                 
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