Using DIMMs of Different Speeds

[Randall Hofland]

I would add to that the obvious: using different sizes of DIMMS (32/64/128/256)
will slow the machine somewhat since the ability to interleave memory access on
some hardware platforms will be disabled. This can sometimes perceptively alter
system speed as the number of DIMMs increases (such as in my PowerMac with 6
pairs of DIMMs) although my PC boards generally allow only 2, 3 or 4 unpaired
DIMMs. I believe this also applies to different CAS rated DIMMS although I
suspect that modern hardware will select the least common denominator (CAS2 or
3).

Mike Bilow wrote:

> It was a myth then and it is a myth now.  Memory runs at the speed of the
> machine, not at the speed of the memory.  If all of the memory is rated
> for at least the speed required by the machine, then it will all work in
> sync at whatever speed the machine operates.
>
> That said, it is a bad idea to mix different TYPES of memory where that
> might be possible for some machines.  For example, in the old days of
> 30-pin SIMM, it was a bad idea to mix 3-chip and 9-chip memory, but this
> was because their timing requirements were different.  In more modern
> 72-pin SIMM, it is a bad idea to mix EDO and non-EDO (FPM) memory,
> although it is possible to run EDO memory at the slower speed of FPM.
> With 168-pin DIMM, there are actually incompatible types which simply will
> not work at all if mixed, such as EDO and SDRAM, and you must get whatever
> is compatible with the machine.
>
> -- Mike
>
> On 2000-05-06 at 20:55 -0400, Chuck Noyes wrote:
>
> > Years ago, I know that using memories of different speeds was a bad idea,
> > but what now?  Is the firmware in PCs these days smart enough to deal with
> > memories of different speeds?
>
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