Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!pyrdc!gmu90x!gmuvax2!smasters
From: smasters@gmuvax2.gmu.edu (Shawn Masters)
Newsgroups: sci.electronics
Subject: Re: QUADRAM MEMORY
Keywords: Speed
Message-ID: <1543@gmuvax2.gmu.edu>
Date: 2 Jun 90 14:24:49 GMT
References: <23502@adm.BRL.MIL>
Reply-To: smasters@gmuvax2.UUCP (Shawn Masters)
Organization: George Mason Univ. Fairfax, Va.
Lines: 36

In article <23502@adm.BRL.MIL> abc@adm.BRL.MIL (Brinton Cooper) writes:
>I purchased a QUADMEG-AT (128K) memory board for an old-ish IBM-PC/AT.
>The board was designed for the 4.77 MHz machine.  However, it turns out
                                ^^^^
>that this machine contains a 12 MHz crystal.
                              ^^ 
The cycle time on the trubo XT's was 150ns.  The original PC used a time
of 200ns(64-256k motherboards, 250ns for 16-64k motherboards).
You might be able to squeak by with 120ns chips on a 12 MHz board, but I
have had the least trouble on this type of system with 100ns chips(plus
the higher speed chips are more reliable due to higher manufacturing
constraints).

>
>The (64K) memory chips in the QUADMET board are 150 ns Fujitsu chips
                                                 ^^^
These will not work unless the board has way of holding the memory wait
line on the bus(unlikely).  You can do some quick work with the
calculator and see why.

>	1. Can I get reliable operation by changing the memory chips?
>
>	2. Is it only the chip speed that is likely to limit things?
>
Since this is a board designed for the XT bus, and you are using an AT
there may be problems.  I'm looking for a description of the AT bus
myself right now, but I don't know enough right now to know if the buses
are incompatible for memory expansion units(not just the bus is at work
here I guess.  What about AT bios and other AT cards?).

You can buy 10-12 MHz boards now for around $100(0k), so if you need the
memory and your going to buy it anyway, maybe it'll be cheaper just to
buy a new motherboard then one of these $200-400 memory expansion board.

Shawn Masters
smasters@gmuvax2.gmu.edu