Peter said:
I am building one, and recently I see there are NVdia cards
that allow the CPU to use the video card to take over some
of its load. What are the keywords required to ask about
this facility when I buy components?
P
More than one company, has the ability to do computing on their
video cards.
The technical terms used might be: GPGPU, OpenCL, CUDA
http://en.wikipedia.org/wiki/Gpgpu
The GPU on the video card, has "programmable shaders". That
thing has been turned into a processor, that is capable of
running short programs. Since there are many shaders inside
the GPU, it is possible to harness many "processors" at the same
time.
About the best speedup I've heard of, is some computing algorithms
are 25x faster when run on the GPU.
But you should also be aware, that not many things see that
level of acceleration. Very few computing problems are
amenable to "infinite divide and conquer". So, smaller
levels of acceleration are to be expected.
And there aren't that many programs which use this feature yet.
There are programming kits, allowing scientists and programmers
to experiment with the capabilities. But it has not reached the
stage, where your copy of Microsoft Word will run 25X faster.
Maybe the latest Photoshop or Premiere might use it. Or
perhaps the latest beta of some open source video compressor.
It's very much a "bleeding edge" technology at the moment.
Not enough people know how to use it.
*******
The thing you see in Windows 7 ("Aero"), involves compositing.
You don't need much of a video card to support that. Apple
was doing that before Microsoft decided to do it, and their
video cards were pretty weak for that purpose.
http://en.wikipedia.org/wiki/Windows_Aero
Pretty much all the OSes have something like that available now.
(Linux has Compiz.)
*******
The video card can speed up other things. The video card
has a playback accelerator for certain movie standards.
Some terms for this: AVIVO, PureVideo, DXVA
http://en.wikipedia.org/wiki/DXVA
This allows a computer with a slightly weaker CPU, to be
able to play HD movies.
*******
The video card speeds up 3D games. You knew that already.
That is Direct3D or OpenGL.
For 2D, the video card supports things like BitBlt ("Bit Blit"),
which is as old as the hills. They don't even benchmark 2D
performance of video cards any more, so this hardly gets
any mention.
http://en.wikipedia.org/wiki/Bitblt
HTH,
Paul