Windows 7

http://windows.microsoft.com/da-dk/windows7/32-bit-and-64-bit-windows-frequently-asked-questions

best forklaret simpelt af microsoft..

Windows 7 Ultimate   
32 bit = 4 GB ram (max)
64 bit = 192 GB ram (max)

Windows 7 Enterprise   
32 bit = 4 GB ram (max)
64 bit = 192 GB ram (max)

Windows 7 Professional   
32 bit = 4 GB ram (max)
64 bit = 192 GB ram (max)

Windows 7 Home Premium   
32 bit = 4 GB ram (max)
64 bit = 16 GB ram (max)

Windows 7 Home Basic   
32 bit = 4 GB ram (max)
64 bit = 8 GB ram (max)

Windows 7 Starter   
32 bit = 2 GB ram (max)
64 bit = N/A ram (max)