The issue with Max. RAM in an Ultra 5 is, IIRC, based on physical size - I seem to recall that there are 256 Meg DIMMs for the Ultra 10 that can be used in am Ultra 5, except for the floppy/PCMCIA adapter cage - if you removed the floppy drive, the DIMMs would fit. I thought the U5 and U10 were based on the same MB...