PC 133 144PIN CL3 SODIMM 256MB.
The CL3 (Clock Latency rating) is the key. Some RAM is simply not labeled with the CL number. (BTW the MPC only reads half a 256MB stick as 128MB by design, the official RAM is actually a 256MB stick too). I never had a stick without the CL rating listed work in an MPC, so specific to a 1000 or 2500 (same RAM spec) I would guess the ones with no CL label are not CL3.
The good news is you can find those for $10 or even less online.
