Limitations imposed by windows 7:
Version........................Limit on X86.........Limit on X64
Windows 7 Ultimate ........ 4 GB .................. 192 GB
Windows 7 Enterprise........ 4 GB .................. 192 GB
Windows 7 Professiona .... 4 GB .................. 192 GB
Windows 7 Home Premium 4 GB .................... 16 GB
Windows 7 Home Basic ..... 4 GB ..................... 8 GB
Microsoft assumes people that run over 16 GB of RAM are probably running (or should be running) the Professional SKU anyway. I'm with them on this one. I can't think of any reason a "Home" computer would need so much RAM, unless you just like high numbers.