On the CyberstormPPC, I think the limit is 128MB. You can, however, add Z3 RAM, so shove a couple of ZorRAM sticks in the machine and you could probably boost over 1GB. However, that increase would come at a cost in performance, since the CSPPC would be forced to access it via the Zorro bus, which is much slower than it's own local memory bus.
OS4 for CSPPC just accepts CSPPC local memory. Motherboad&Zorro memory modules are completely ignored. Joerg Strohmayer decided that Motherboad&Zorro memory support should be dumped in favour of swap memory (even thought no OS4 classic version with stable swap existed)
