The Max memory is limited by the chipsets on the laptop/ Desktop motherboard not the OS.
Windows 7 x64 can use upto 192 Gig. The laptop can only handle 4 Gig.
Most motherboards have a memory capacity of 8 to 24 Gig. Servers can handle alot more RAM, up to 256 Gig. Most laptops max out a 4 Gig.
Most laptops have 2 memory slots, Most slots on laptops max out on 2 Gig per slot. some max out at 8 Gig.
Most desktop boards with 4 slots max out at 8 Gig
Most desktop boards with 6 slot max out at 16 Gig or 24 Gig.
Plus Some chipsets have limitations on the amount of RAM that they can support. The ASUS CUSL2 motherboard had the Intel 815 chipset that could only support 512Meg of RAM, So they only put 2 slots on the motherboard.
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
These limits are similar to those for Vista editions, expect that Vista Enterprise and Vista Ultimate have had their upper limits raised from 128GB to 192GB.
The one to look out for there is the 16GB limit on Home Premium. If you’re building a Core i7 system then it’s quite easy (if you have the cash!) to exceed this limit. As long as you’re aware of the limit and plan your OS accordingly you’ll be OK.