Adding old PC100 DIMMS alongside newer PC133 - OK?

[Lobster]

My kids have a pretty old PC (a P4 1.6MHz) which has a single PC133
DIMM module fitted (128 or 256Mb, can't remember). I happen to have
two old 64Mb PC100 DIMMs from an old PC kicking about at home - would
it be OK/feasible/sensible to fit these in the two vacant slots on the
kids' mobo? I realise the old memory is slower, but would that
nevertheless be compatible with the newer DIMM? Or could doing this
slow the whole machine down?

I appreciate that it would be best to buy new memory but I don't want
to spend money on such an old PC - the current suggestion is a
zero-cost option.

Thanks
David

 

[Tony Hill]

My kids have a pretty old PC (a P4 1.6MHz) which has a single PC133
DIMM module fitted (128 or 256Mb, can't remember). I happen to have
two old 64Mb PC100 DIMMs from an old PC kicking about at home - would
it be OK/feasible/sensible to fit these in the two vacant slots on the
kids' mobo?

In a word, no.

I realise the old memory is slower, but would that
nevertheless be compatible with the newer DIMM? Or could doing this
slow the whole machine down?

It would slow the whole machine down... to a complete stop. P4's
using Intel's i845 chipset (the only common P4 chipset to use SDRAM)
absolutely require PC133 memory. If you put PC100 memory in the
system it probably won't boot at all.

Even if it did boot, it would slow the system down by about 25%. The
P4 on the i845 chipset was BADLY starved for data from it's PC133
memory. That memory was just way too slow for the processor. If the
system would work with PC100 memory it would make this data starvation
just that much worse, slowing everything down in the process.

I appreciate that it would be best to buy new memory but I don't want
to spend money on such an old PC - the current suggestion is a
zero-cost option.

You might be able to find some second-hand PC133 memory for
dirt-cheap.