Memory Limits for Windows

Physical Memory Limits: Windows 7

The following table specifies the limits on physical memory for 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 Professional 4 GB 192 GB
Windows 7 Home Premium 4 GB 16 GB
Windows 7 Home Basic 4 GB 8 GB
Windows 7 Starter 2 GB N/A

for information on other versions of Windows see here : Memory Limits for Windows Releases