Quick question here guys, and I know i'm asking the right crowd.

For your everyday, DirectX using, 3d games you buy today,games from around 2001 to now, you sometimes see in the options, to run the game fullscreen or windowed.

However I never figured it out, which would make a game run BETTER? Which gives better fps, which makes the cpu drag less, and which requires less ram? Or does it make any diffrence?

Say I have a game running 800x600. Which will make the game run smoother, fullscreen or windowed? I assume fullscreen, but I've never actually been TOLD one way or another, which is better?

Full screen always give better performances. I have no idea whatsoever why some people would want to play in windowed mode, but there should be a good reason.

yes, there are- if your teacher is somewhere behind you and you can cover this small window, with your body during the lesson =)
but its slower of course

I think that full screen mode should be faster, because if you run an 800x600 game and your desktop has more pixel it will be setted in the low-res to be played in full screen, so the graphic performances speed up!

on slower computers, ruinning a direct3d or openGL game will run smoother when in windowed mode. Don't ask me why, but it always has, and you will get better FPS. It may also be coincidental, but I also found that when playing multiplayer games, a window will hold a better ping.

for me a small screen is in some games much much faster

well not for me
it is logic to run fulscreen faster, cuz if you are in windowed mode then computer needs to "draw" antoher things (desktop, other windows, or anything else you run) too
when running in fullscreen it dont need to

You might want the game in a window if you don't want the display to change to the game's resolution everytime you start it. It also makes for easier task-switching (switching from a windowed game to the desktop doesn't take as long as from a fullscreen game).

Depends what you need it for. For example, you can be using a walkthrough or trainer or chatting on MSN or in class or playing a soccer manager game that doesn't need to be fullscreen...

But for shooting games you must use fullscreen since the mouse can cause havic on the side of the window :P

The logic behind this is if you play a game in Windowed mode, the computer need to recalculate everything (graphical wise) depending of the size of the window instead of having it directly set as "default" in fullscreen. At least that's how it work for most old games, and this can be a very tedious task for your CPU (thus eating ressources) unless you have a good graphic card installed on your system.