BIOS Setup displays 3072MB system memory size, although 4096MB memory is installed on the motherboard.
Please confirm the correct information using VAIO Control Center
1. Click Start - All Programs
2. Click VAIO Control Center - System Information
3. Double-click the System Information option and verify the memory information.
You also can visit http://support.microsoft.com/kb/929605/en-us for further information.