GetTickCount on dual core machines
 

I'm using the Win32 API call GetTickCount for various high speed uses in C++
and Delphi native code. We've noticed that on some systems, this is very
accurate (as you'd expect) but on other systems it can lose as much as 30-60
minutes a day. We're using a combination of machines, Pentium 4 2.8GHz and
Intel i3 dual core (2.40 GHz) but no clear indication which machines are
better and which are worse.

My question is:
* What causes a computer to lose time over a day?
* Will installing extra hardware (such as a PCI USB expansion card) affect
this?
* On a dual core processor, does each core have a separate TickCount or is
there one TickCount for the machine?

Thanks,
Alain