RAM Myth???

I was in the lab yesterday at the university and was messing around with tweaking RAM. We were overclocking DDR333, DDR400 and a few other old sticks of RAM to the point where they were smoking. Was doing some research and getting in more detail about overclocking RAM.
I was talking with my lab partner who told me that in your system settings, if you have 512MB of RAM and windows says you have 523,760KB RAM the reason its not a full 512MB is the quaulity of the RAM. Opposing to his system at home where he has 2gigs of RAM it says he has the full 2gigs of RAM. I wanted to find out from you guys if this is true. This is not the first time I have heard about this.
Also the factor of shared memory for video is not a factor. The system with 512MB RAM was running a Nvidia TI4600 128MB video card.

ZiPPy

heard that one too ...
at home i use 2 x 256 sticks and it displays the full 512 of RAM. (RD slots)

Now i again use 2 x 256 DDR in the office and guess what .... i obtain only 480mb of available ram ( under both linux and winXp)
using a 64mb graphics card...

When asked to the supplier he straight away went to the shared video memory theory where

available ram = 480 MB
another 32 Mb for the video and voila it makes 512 Mb !!!!
but what abt the 64 MB on my graphics card .... ?????

Sir i dont know abt the graphics card but all i can tell u is that the your system is sharing 32mb of my RAM sticks :!:

May be these links will shed some light. I don't know. Right now I'm going through them.

forums.pcper.com/showthread.php?t=320351

forums.extremeoverclocking.com/showthrea...DDR333+DDR400+Issues