I have a Latitude E6400 running XP Pro SP3.  I replaced the 1 gb DIMM in it with (2) 2gb DIMMs.  DDR2 PC2-6400.

The BIOS recognizes all 4 gig of RAM.  Windows doesn't, it's showing 3.45 gig.  I haven't checked yet, but it's possible that some of it is being used/shared for video.  But over a half a gig?

Why would the BIOS report 4 gig, and Windows less than 3.5 gig?