4.00 GB (2.99 GB usable)

Problem
- I am using Windows 7 with 4GB of RAM but system properties says 4GB RAM(2.99GB Usable) ...
- Installed 4GB RAM but the windows 7 says Usable 2.99GB RAM
- Windows 7 shows 4.096 GB(2.96 GB Usable) memory
- Why the Windows 7 memory (RAM) 4 GB (3.25 GB usable) ...

Clean Solution
You need to install Windows 7 - 64 bit

Technical Answer
A 32bit desktop windows 7 can just address 4GB of memory addresses.
This memory is include RAM + other hardware memory like Graphic Card,
Then if you have
4GB RAM + 1GB Graphic Card Memory = ~3.0 GB RAM available
4GB RAM + 512MB Graphic Card Memory = ~3.5 GB RAM available
and etc...

Physical Memory Limits: Windows 7

The following table specifies the limits on physical memory for Windows 7 [link]

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