AGP vs. PCI?

M

mavic19

New Member
#1
What are the differences between PCI and AGP video cards. Which one is better?
 
D

deth666

New Member
#2
The AGP Bus runs at 66mhz (133 in 2X mode) unlike the PCI Bus which runs at 33MHz
also the AGP bus has direct access to system memory to store textures, the PCI bus doesn't

AGP is Better.
 
C

collinj

New Member
#4
Something to consider is that not all AGP cards really support the AGP bus specification, and are basically nothing more than PCI cards on a faster bus.

The AGP port is always 66mhz (unless you run your bus at 75/83/112/124/ bus speeds). AGP 2x shows that a card can transfer information at 2x the normal AGP transfer speed because it can transfer data 2 times per clock cycle (which is the 2X), but the card does not actually run 133mhz. I dont remember what the number is exactly, but it works out to around 500mb/sec memory bandwidth between the video card and the system memory. The thing here is that the Video card has to support DME. DME is Direct Memory Execution, and refers to using the system memory directly for texturing.

When looking at an AGP card, the box may say, AGP 2x with Sideband support, when the card actually does not utilize DME, so the AGP spec is pretty much useless here. The card is not capable of directly accessing the system memory for texture storage, but it does load the textures to the card faster on initial load up than a card that does not support AGP 2x and sidebands, but if the texture load increases past the memory available on the card, this type of card will slow down considerably compared to a card that allows DME of textures.

Not many games right now utilize this feature, but more are coming allong that do, and they will get a boost in performance.

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Collin J
HWC Administrator
Moderator: Support and General discussion.
 
R

Rob Williams

New Member
#5
Ah, I knew AGP was 66Mhz, and couldn't fully work out that 2x stuff. I'm learning fast all the time. Thanks.
I still say Go AGP though.
 

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