The AGP AND PCIe bus...

[imported_goku]

Ok I hear time and time agian about how critical it CAN be to have onboard video memory instead of using system memory and that having a bus faster than AGP 2X isn't really needed because all the info is stored on the onboard memory. But here is the thing, if you lack onboard memory and your running a game that requires quite a bit of memory, wouldn't the bus speed become a siginificant factor in your game speed if you lacked on board video memory? Isn't the the Aperture Value in the registry directly referring to this? I'm just a little confused about this all and having this clarified would be great.

 

[Lonyo]

When a game needs more memory than the card has itself, it swaps out with main system memory over the AGP bus.
The AGP paeture is, IIRC, the amount of RAM which can be used for extra textures if needed (ie: if you have a 128MB graphics card and 128MB AGP Apeture, you can use an extra 128MB f system RAM if extra space is needed).
Obviously the transfer is done across the AGP bus, so a slower bus could give slower speeds, but getting stuff from the system RAM is slow anyway.

 

[mwmorph]

?
AGP2x is crap. AGP4x is somewhat of a bottleneck now.
AGP8x is a good sped ofr current games.
first, if the card runs out of memory and has to fetch from the AGP apature too much, you're royally fuuked either way. as for pure bus bandwuith, the texture fetches should not be big enough to saturate either pci-e or agp bus thus not really increasing performance on the pci-e platform.

 

[otispunkmeyer]

basically in a short answer

if you have no on board memory on a AGP card, you are then going to be forced to use the Apature memory allocated in the BIOS, which is basically an amount of system ram that can be used to store video data, and because the only way to reach this memory is across the system bus or AGP bus, then yes buss speed would become a factor.

its a reason on board memory is so bad for gaming, since it has none of its own memory. and it has to use the small bandwidth (in relation to normal GFX cards) to store its data. not to mention most integrated solutions are just flat out crap anyway

 

[imported_goku]

Originally posted by: mwmorph
?
AGP2x is crap. AGP4x is somewhat of a bottleneck now.
AGP8x is a good sped ofr current games.
first, if the card runs out of memory and has to fetch from the AGP apature too much, you're royally fuuked either way. as for pure bus bandwuith, the texture fetches should not be big enough to saturate either pci-e or agp bus thus not really increasing performance on the pci-e platform.

Ok so I guess it's not a matter of saturating the bus, but a matter of lantecy of moving it back and forth+ the lack of bandwidth the system memory has right? Well if it's not bandwidth, then how come when you increase the memory bandwidth on a video card, there is significant performance improvement?

 

[mwmorph]

Originally posted by: goku

Originally posted by: mwmorph
?
AGP2x is crap. AGP4x is somewhat of a bottleneck now.
AGP8x is a good sped ofr current games.
first, if the card runs out of memory and has to fetch from the AGP apature too much, you're royally fuuked either way. as for pure bus bandwuith, the texture fetches should not be big enough to saturate either pci-e or agp bus thus not really increasing performance on the pci-e platform.

Ok so I guess it's not a matter of saturating the bus, but a matter of lantecy of moving it back and forth+ the lack of bandwidth the system memory has right? Well if it's not bandwidth, then how come when you increase the memory bandwidth on a video card, there is significant performance improvement?

because the video card memory bandwith is use fore more than just fetching textures(only use for AGP aperture, i think is to write textures that dont fit in local memory to system ram). anyway effects like AA require high memory bandwith frok local memory.

 

[superfly27]

I don't want to ignore everything that was said here but just want to add...Nvidia said they no longer plan on making AGP video cards.

The cost of replacing a motherboard now might be justified because you won't have a problem upgrading later.

 

[TerracideDK]

The PCI-E slot also delivers more power than an AGP slot...

Terra...

 

[jiffylube1024]

Originally posted by: TerracideDK
The PCI-E slot also delivers more power than an AGP slot...

Terra...

Yes, but power has no bearing on performance whatsoever, it just means that some cards (eg the 6600GT) don't need external power connectors on PCI-e, while other cards can get away with one external power connector instead of two.

Originally posted by: goku

Originally posted by: mwmorph
?
AGP2x is crap. AGP4x is somewhat of a bottleneck now.
AGP8x is a good sped ofr current games.
first, if the card runs out of memory and has to fetch from the AGP apature too much, you're royally fuuked either way. as for pure bus bandwuith, the texture fetches should not be big enough to saturate either pci-e or agp bus thus not really increasing performance on the pci-e platform.

Ok so I guess it's not a matter of saturating the bus, but a matter of lantecy of moving it back and forth+ the lack of bandwidth the system memory has right? Well if it's not bandwidth, then how come when you increase the memory bandwidth on a video card, there is significant performance improvement?

The reason increasing memory bandwidth on a video card improves performance is because this is the RAM that is used in games and 3d applications; increasing the system's memory bandwidth doesn't have a dramatic improvement on games because if the video card runs out of local (on-card) memory and needs to go through the AGP or PCI-e bus, that slows everything down tremendously.

Basically, AGP memory (ie the AGP aperture memory) is a last resort that only is accessed in worst-case scenarios. This is why setting large AGP aperture sizes (ie 256MB or more than 256MB) is unnecessary and just wastes system memory. If the game is using so much memory that it constantly uses up all available local (on-video-card) memory, then performance will be terrible.