How does a CPU bottleneck a Graphics Card?

Over and over again I hear people saying that CPU's could bottleneck your graphics card. How does this work? What causes the bottleneck and such?

i don't know, its the first time i heard of it. from what i heard, the cpu isn't as important as the video card in games, but if you have a low end cpu and a high end video card, that may be the reason for the bottleneck issues.

Well I understand that when you have a P4 and a 8800GTX your processor is bottlenecking your graphics card. But why? Is the processor not keeping up with the info the graphics card is sending? I'm gonna try to find a really in depth answer somehow!

Yea me to, im itching to buy a Gigabyte DS3L and an e7200 but am not sure if it would even be worth it with my card. ALTHOUGH i do plan to get one of the new 4870's coming out if there up to par where they should be.

The video card doesn't know anything about the game you are playing.. Where the trees are, who is shooting at you, what is gravity (well maybe these days they know), what color things should be, and basically WTF are you asking it to do?

The CPU and the rest of your system use the graphics card to draw all that stuff, but something still has to create it, and tell the GPU what is going on.

Most of that stuff is constant, which means that the CPU has a 'fixed' load on it, to some degree. That's why raising the resolution or rendering detail increases the load on the GPU compared to CPU..

If that doesn't make sense, let me know and I'll try again..