Can I use a 128MB PC100 SDRAM DIMM with a 128MB PC133 SDRAM DIMM? Answer:: Generally you can mix PC100 and PC133 memory in the same system. The faster memory will run at the slower memory's speed (in this case PC100). However, there are some systems that will not correctly run this memory configuration. It is rare, but we suggest you contact your computer manufacturer or motherboard manual for specifics.