OS MaxRAM (mobo BIOS limits may be less)
XP(32-bit) - 4GB
XP(64-bit) - ??GB
Vista Starter edition - 1GB (deliberately crippled)
Vista Home Basic, Premium, Business, Enterprise, Ultimate - 4GB
(4GB is an 32-bit limitation that applies to any 32-bit OS, like the 32-bit Linuxes)
Vista x64 Home Basic - 8GB
Vista x64 Home Premium - 16GB
Vista x64 Business, Enterprise, Ultimate - 128GB
(any 64-bit OS, like 64bit Linux or Solaris, can theoretically support 17,179,869,184GB or 16 exabytes of RAM)
[Actually 32-bit OSes
can address up to 64GB using Physical Address Extension (PAE) which pages memory in and out rather like the old LIM expanded memory in the dear old DOS 640KB memory days, but we won't go there!]
The cool thing about Vista is that it needs 2GB of memory to do (slowly) what XP does reasonably quickly and the 32-bit Linuxes pretty fast in 512MB....
