XP not detecting all my installed RAM

[Refwhett]

I have 4 x 1gigs of RAM (DDR2-SDRAM PC2-6400 (399 MHz) - [DDR2-800]
) intalled on a Asus P5N-E SLI.
The bios detectsw 4 gigs, PC Wizard 2008 detects 4 gigs and yet windows and "ram managment software" detect only 3,5 gigs.
Why is that and where did 0.5 gigs disappear?

thx.

 

[SittingDuckie]

I assume your using XP or vista 32-bit? 32 bit operating systems can only manage up to approx 3.5 gigs of RAM. You need to upgrade your operating system to a 64-bit OS in order to use the additional 0.5 gigs of ram.

 

[Refwhett]

Oh, darn. I guess I'll wait with that then.
Thank you for the quick reply.

 

[skitzo_zac]

Yeah as SittingDuckie said you must be running a 32bit version of XP. For your OS to detect the full amount (4GB) of RAM you must upgrade to a 64bit OS.