This is not really hardware, but:

I have 512mb ram in my computer, and I'm using Win XP Home. So, when I check memory in task manager, it says there's about 330mb ram free (just turned the computer on, no programs started yet, except background stuff). Ok, it may be that virus protection, firewall, drivers and windows take 200mb of memory, but when I calculate the memory usage from the 'processes' section in task manager, I only end up on something like 130mb. So, what uses that something 70mb of memory? Because it's no process which is in task manager, but it's not free memory either.