How to Check RAM Size without Looking at Motherboard
Solution 1:
It's because your OS is 32-bit. Check out Dude, Where's My 4 Gigabytes of RAM?
Solution 2:
http://www.cpuid.com/cpuz.php
This will tell you everything about the memory installed in your machine along with the cpu. It will show which slots contain what size sticks and what speed they are running at.
The link JP posted from coding horror explains exactly why you only see 3.5gb out of the 4 you have installed is because of a 32bit OS.
Solution 3:
Because you are running 32Bit Windows 3.5GB is the maximum amount of RAM you can support.
A 64bit Operating system is required to use any more RAM. So currently you are wasting 512MB of RAM.
Solution 4:
4GB Ram is the maximum allowed in 32bit operating systems.
I suspect that because your Video Card uses 1/2GB, that leaves 3.5 GB left.
Solution 5:
Check memory with memtest86
- web site
Or use Everest or other hardware recognition software
- Everest web site
UPDATE:
Your question is wrong. Better is "Why my XP see only 3.5GB RAM?"
Answer from JP is right