Windows 7 showing Different Installed (4 GB) and Usable Memory (2.96 GB)
Installed and Usable memory as shown by windows differs when you have installed a Graphics card which shared memory. If you have a graphics card of 1gb memory with shared option, the 1 GB of memory is not usable by other processes. So the usable memory is lower than that is installed.
The above screen shot is from Windows 7 Home on a Dell Studio 15 laptop, with 4 GB installed RAM and an NVIDIA Graphics card with shared memory of 1 GB. Therefore only 2.96 GB of the RAM is usable by the processes.
It is better to buy graphics cards with Dedicated memory even if the memory size is less than that is being shared from RAM. This is because, in shared memory the memory buses might be mostly occupied by the graphics system that can slow the system down. In dedicated memory this problem is avoided because the RAM is not touched for graphics rendering and hence the bus is free for your processes.19 Feb, 2010