While the maximum RAM limit for 32-bit Windows 7 editions is 4GB, when it
comes to the 64-bit editions, the amount of memory that the OS can address
depends on which edition you are running.
Here are the upper RAM limits for the different editions of Windows 7:
Starter: 8GB
Home Basic: 8GB
Home Premium: 16GB
Professional: 192GB
Enterprise: 192GB
Ultimate: 192GB http://www.zdnet.com/blog/hardware/max-memory-limits-for-64-bit