Discussion: AGP 8X & 256bit memory interface.

[lhgpoobaa]

well as seen in comdex there are a smattering of AGP 8X comming out.
the R300 will have it
and certain types of the Xabre might (who knows whats happing there)

but is agp 8x really needed? when do we ever see a geforce4 4600 maxxing out the AGP 4x bandwidth?

and im curious about the 256bit DDR ram interface on the Xabre.
are the Ram chips themselves 256bit, or are we looking at some form of quasi 'dual channel' setup wehere the ram is divided into two 'banks'?

hmmm

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[chuck232]

I didn't know that the Xabre had 256bit DDR RAM?? I know the Parhelia/R300/NV30 are supposed to. Basically it allows larger "packets" to be passed to the memory at a time. Therefore an increase from 128bit DDR to 256bit DDR should theoretically double the bandwidth of these awesome cards.

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[chuck232]

WEll just thinking about this one again. The GF4 Ti4600 does max out at some games at hihj resolutions or with AA. So maybe with AGP 8X, you'll get even faster speeds. Just a thought, cause theoretically you would. (been using that word a lot...)

My firewall tastes like burning.

 

[lhgpoobaa]

i believe thats still internal GPU to RAM bandwidth limitations again
all the calculations and texture stuff is happening onboard.


<font color=blue>Pants Down! Turn Around! Bend Over! You're about to Experience Telstra broadband! :lol:

 

[Crashman]

The latest cards may FINALLY APROACH using the full bandwidth of AGP4x, AGP8x is not usefull at all. But the 256 bit memory interface will help a great deal.

What's the frequency, Kenneth?

 

[phsstpok]

The problem is that most games are designed to avoid pushing AGP bandwidth. The reason for this is that there are a variety of graphics cards that must still be supported by the games. Those cards short on memory might have to access textures that are stored in system memory. Accessing this memory with using AGP's piddly 1066 MB/sec bandwidth (at 4x) would be bad enough but the application also has pass the vertex information sharing that bandwidth.

AGP crawls compared to a graphics card's local video bandwidth of 2800 MB/sec up to 9600 MB/sec and higher. Game designers are forced to keep the polygon counts low because if they push the limits then all users would see significant slowdowns not just users with low-end video cards. Textures can be reduced in complexity and colors so that for a given scene the textures fit in the video card's local memory which cuts down on AGP bandwidth usage. New textures can be loaded between scenes when pauses and delays are expected. This leaves most of the AGP bandwidth for just vertex information. The polygon (and thus vertex) counts are kept low to keep some of the bandwidth open for textures if needed. (Some games do a better job at keeping the balance, games like Serious Sam 1 & 2).

FPS games barely push AGP 2X for the reasons mentioned above. Similarly, in the near future games will only push AGP 4X. When that happens, low memory, 4X, video cards will be left behind because there will be little AGP bandwidth headroom for textures.

On the other hand, I remember reading that flight games do push AGP 4X. I don't know that it is true but I would imagine real-world terrain requires a very high polygon count and a significant number of textures as well.

Perhaps someone can confirm this.

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[eden]

Doom III is one game that will definitly push the AGP...

--
Meow

 

[chuck232]

Also with the 256bit mem, the bandwidth shouldn't be as big of a concern, therefore the AGP bandwidth may affect the performance of the video cards. With AGP8x, it should free up way more bandwidth. It's always better to have more than too little I find. DoomIII's graphics look so very amazing. I wasn't able to download the gameplay clip, but I saw some screenshots and by golly, the graphics look friggin sweet.

My firewall tastes like burning.