Date: Sat, 22 Jun 1996 15:26:26 -0700 From: "Michael L. VanLoon -- HeadCandy.com" <michaelv@HeadCandy.com> To: nash@mcs.com Cc: freebsd-hardware@freebsd.org Subject: Re: Mixing SIMMs of different speeds Message-ID: <199606222226.PAA11560@MindBender.HeadCandy.com> In-Reply-To: Your message of Sat, 22 Jun 96 17:21:04 -0500. <199606222221.RAA06668@zen.nash.org>
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>> >I'm wondering if I can mix 60 and 70ns SIMMs. Everyone says don't,
>> >but they don't say why. I can understand not mixing SIMMs that will
>> >be accessed simultaneously (like banks 1 and 2), but why shouldn't it
>> >work when they are separated? My motherboard's manual indicates 70ns
>> >or faster will work, so why wouldn't a mixture?
>> Probably because the people who designed your motherboard designed its
>> timing parameters with the assumption that all your memory would
>> display consistent behavior.
>The question is what behavior is it expecting? If it expects the data
>to be valid within 70ns, it is consistent.
Exactly.
>> Another thing is that some motherboards will do interleaved access if
>> you have matching size SIMMs in all the slots. This is where it
>> alternates between accessing bank 1 and bank 2 on even/odd memory
>> accesses.
>Aren't both banks (1&2) accessed simultaneously for any 32-bit access?
>When you said all slots, you mean groups of two, right?
I was going under the assumption that one "bank" consists of the
smallest usable memory size, i. e. two 72-pin SIMMs. So, bank 1 is
the first pair of SIMMs, bank 2 the second....
>> If it were going to work at all, that would be my suggestion: put the
>> slower memory first, so if it does some sort of test to see how fast
>> your memory is, it might use the slower memory for the timings. Note
>> that this is highly speculative and implementation specific. Only the
>> people who designed your motherboard can tell you for sure.
>Good, so I'm not crazy for thinking this might work :)
Right -- this is what I would expect. But there's still no guarantee.
Some engineer may have found it more useful to test, say, the last
SIMM installed. How can we know without asking him?
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Michael L. VanLoon michaelv@HeadCandy.com
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