Depending on where you are looking, the total amount of memory installed in the system will vary. If the BIOS read all 512MBs and the system properties shows 312MBs then either you have Windows 98SE or you have a 128MB onboard video card which will account for part of the memory but not all. First check the BIOS and make sure it is reading all of the memory.
Crucial Performance Lab
The Memory Experts(SM) at Crucial Technology is now on board to give you straight answers to your memory-related questions.
When responding please provide your full system specs; hardware and software, OS, BIOS, drivers Etc. You can e-mailmemory related questions to firstname.lastname@example.org