overclocking IIsi, is RAM speed in the equation?

[lowlytech]

Was about to swap out the 40MHz crystal for a 50MHz to overclock the 030 CPU to 25MHz and wondered how much memory speed timings played a role in the overall stability of this particular overclock mod.  I have two IIsi boards and one actually has -70NS onboard RAM instead of the standard -80NS RAM, however the logic board that has the -70 ram is in worse shape than the other.  I knew in PC days when you overclocked the CPU it also bumped the ram frequency up as well.

 

On the subject, I have a nubus copro adapter as well that has a 20MHz copro on it.  I assume one doesn't normally change that crystal out as well or has anyone overclocked the coprocessor as well?  It had a 40MHz crystal on the adapter board as well.

 

 

[Fizzbinn]

I don’t think you need to worry. The IIsi is based on the the IIci architecture, the IIci runs at 25Mhz and only requires 80ns RAM. I’ve made the 25Mhz mod on two IIsi boards without a problem.

 

I also haven’t had a problem using a IIsi NuBus adapter in these systems, the 68882 FPU math coprocessor on the adapter apparently picks up the clock from the motherboard and also runs at 25Mhz. I’m guessing the clock crystal on the adapter may be for the actual NuBus bus? See the IIsi benchmarks I did in the following post which illustrate FPU performance increase with the 25Mhz motherboard mod (with and without a 68882 from a NuBus adapter):

 

 

[lowlytech]

Thanks Fizzbinn for the peace of mind.  I will try this overclock on the better condition board and see how it works out.  Also thanks for the link, looks like some good benchmarking in there.  Always love reviewing stats on different machines.