I have a RS/6000 B50 (rackmount version of the 43p/150). I know it takes PC100 168-pin ECC Registered DIMMS, as I have one 128MB stick in there now from the parts bin, but that's my only one. I'm trying to get some more memory to make it useful, but local suppliers only have 512 and 1GB sticks, and per IBM 4x256 is the maximum supported memory. Does anyone either have 256MB DIMMS to sell or know if the machine will use larger capacity DIMMS?