DirectX vs. GDI

[joezhou]

I have post this message on VC++ before, remembered there was only one guy given the answer, and tell me something about this theme. But I think that's not enough.
What I asked before is "why the DirectX is faster than GDI", the guy with the kind heart told me that because there were less layer in DirectX than in GDI.
I agree with the standpoint, but I am sure there must be other things make the DirectX different from GDI. I am eagle to know what they are. Then when I am implementing some inferfaces for some specified systemes, I have had the key.
Any answers, include web address, articles and tips will be appreciated. Thanks!

[galathaea]

A brief discussion on this can be found at this newsgroup posting (http://groups.yahoo.com/group/delphigames/message/6551). It may go over what you already know, but the points include:


DirectX runs more of its time in kernel mode directly interacting with the hardware, where as GDI must go through an executive redirection (this is less of a problem on Win2000 and above business Windows versions).
DirectX will try to optimize itself for available added hardware, whereas GDI continues (for the most part) to try to be hardware independent.
Finally, DirectX uses a much more optimized drawing model to speed up the time from display/draw call to output.


I hope I have been able to provide some help to your question!