Dear Vinod,
Thank you for your kindly mail and inquiry. About the issue you mentioned, the reason you lack of memory can be related to the processor. Core i3 540 Clarkdale will consume the memory, thay why only 3.87GB is usable. If you try a Lynnfield processor, like Core™ i5-760 2.80GHz, then it won't have this problem.
If you still have any further question or suggestion about our products/service, please do not hesitate to contact us. We will try our best to help you resolve the problem ASAP.
Regards,
GIGABYTE TECHNOLOGY