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Mixing RAM types in an AST Six Pack Plus?

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themaritimegirl

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The AST Six Pack Plus (long version) in my IBM XT has four of the six banks populated with 4264 chips. I would like to populate the remaining two banks, and have the opportunity to purchase some Fujitsu 8264 chips - which are listed as compatible in the SPP's manual. Is it okay to mix the two types of RAM? I know both are 64k x 1 - I just want to make absolutely sure before I spend money. :rolleyes:
 
TheMaritimeMan said:
Is it okay to mix the two types of RAM?
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For vintage computers, I do not see any reason to use the the same make and model of RAM. Adhere to speed and compatibility, and that should be enough. I have mixed RAM chips many times without problem.

'Modern' computers are different. The BIOS interrogates the RAM to get the RAM's timing parameters then adjusts the motherboard's RAM timing accordingly. I can just see a BIOS author getting their code to interrogate the first SIMM for timing parameters, then making an assumption that the remaining SIMMs are the same. The assumption would be based on the fact that the motherboard manual indicates that same make and model SIMMs are to be used. Something like that.
 
Hmm, timings... AST's manual states to use 200 nS RAM. The RAM already in mine is 150 nS, and the RAM I might buy is 200 nS. Do you think it's safe to assume that the card always runs at 200 nS (seems reasonable to me that 150 nS RAM would also work at the slower speed), and so there wouldn't be any issues there?
 
TheMaritimeMan said:
Hmm, timings... AST's manual states to use 200 nS RAM. The RAM already in mine is 150 nS, and the RAM I might buy is 200 nS. Do you think it's safe to assume that the card always runs at 200 nS (seems reasonable to me that 150 nS RAM would also work at the slower speed), and so there wouldn't be any issues there?
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The RAM timing used in the IBM XT is fixed, and for the timing used, IBM have calculated that 200 ns RAM is required.
The situation is similar to the speed rating on your car's tyres. You have the option of putting on faster rated tyres, but your car will not go faster as a result.
So the wording used by motherboard and card manufacturers if often like, "Use 200 ns RAM, or faster."
Yes, 150 ns is faster than 200 ns. Confusing because we are actually talking of a time period, not a speed.
 
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