What Happened to AGP Slot on new mobo?

  • Thread starter Thread starter Red Cloud
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Red said:
How comes new mobo does not come with AGP slot?
Click to expand...

Replaced by the (slightly faster) PCI Express.

AGP is a point to point interface, with a fairly
nasty I/O. The nasty part, comes from some of the
poor chips designed to work with it. The fastest
AGP in practice (not some imaginary standard), was
AGP 3.0 at 2133MB/sec. AGP signal quality, only
became good, just as AGP was being phased out. You
could almost depend on it to work then.

http://en.wikipedia.org/wiki/Agp

AGP actually consisted of two protocols. Slower transfers
are used for the baseline interface. Faster transfers
are done for burst transfer operations (as far as I know,
these are similar to DMA). So when I give a number like
2133MB/sec, not all the operations on the AGP bus happened
at that speed. Some of them were considerably slower. If
you installed the "PCI driver" for your AGP slot, then
you can test what it's like to use only the slower transfer
mode.

*******

The replacement is PCI Express. PCI Express uses up to
16 lanes running at 500MB/sec serially. That is 8GB per
second. In addition, unlike AGP (which is simplex), PCI
Express is duplex - you can do simultaneous data transfers
in both directions at the same time. So in theory, you can
double the bandwidth number again (to 16GB/sec). But in practice,
you're likely to find a dominant transfer direction,
so 8GB/sec is a better estimate of useful transfer
rate.

That is an interface using Revision 2 rates.

The original revision of PCI Express, runs at half that speed.
So that one, when 16 lanes were wired up, gave 4GB/sec,
compared to the 2.133GB/sec of AGP.

Is the bandwidth put to good usage on a video card ? Not
really. It's rather a waste. In this updated review
of PCI Express, they turn off some of the lanes, and
gaming performance isn't affected until a *lot* less
bandwidth is available. Video cards have so much RAM
on them internally, you can load all the textures you need,
before a game level starts. Exceptions to that, might be
Microsoft FSX flight simulator, where textures or content
are paged in continuously. For a lot of canned content,
the content can be cached in video card memory, before the level
starts.

http://www.techpowerup.com/reviews/AMD/HD_5870_PCI-Express_Scaling/24.html

Paul
 
Red said:
How comes new mobo does not come with AGP slot?
Click to expand...

BTW. The last motherboard I know of, to have AGP,
has an LGA775 processor socket. But it finally
went out of production a few months ago. I bought one
of these, and it has pretty slow memory options. But
if you had an old AGP card, it worked fine with that.
I had many happy hours gaming with this.

ASRock 4CoreDual-SATA2 R2.0 - about $66 or so
http://www.newegg.com/product/product.aspx?item=N82E16813157115

It is limited to FSB1066 processors. People have
put quads in it (Like Q6600). I ran a dual core in
mine.

The board actually has two video slots. The brown
one is AGP. The purple one is PCI Express x4 (slow).
The slot spacing, doesn't make it practical to run
two video cards at the same time. But it was still
a damn fine motherboard for $66 at the time. It
also has lots of legacy interfaces, like a parallel
port, serial port, PS/2 connectors and so on. Two
IDE connectors, two SATA connectors. A mix of the old
and the new world.

Paul
 
Replaced by the (slightly faster) PCI Express.
Click to expand...

The fastest PCIe x16 display cards should be faster than the fastest AGP
card...

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Man-wai Chang said:
The fastest PCIe x16 display cards should be faster than the fastest AGP
card...
Click to expand...

My point was, it has more to do with the power of the GPU,
than with the bus bandwidth.

The bus is still faster than it needs to be. You can cut the
bus bandwidth in half, and hardly notice any change in rendered
frame rate.

The techpowerup article makes the point, that it's OK to own
a motherboard with two x8 slots, because the reduction in
bandwidth hardly matters at all. (Some motherboards don't
automatically switch between x8/x8 and x16/x0 mode because
they lack lane switches or a paddle card for routing the
PCI Express tracks. A fixed x8/x8 wiring pattern is OK,
since it has a small effect on the results.)

Paul
 
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