ATI Radeon HD 2900 XT: Calling a Spade a Spade
by Derek Wilson on May 14, 2007 12:04 PM EST- Posted in
- GPUs
Finally: A Design House Talks Cache Size
We're quite used to talking about cache sizes on Intel and AMD CPUs, but graphics hardware has been another story. We've been asking for quite some time, while other sites have taken to writing shader code to come up with educated guesses about how much data fits on die. Today we are very happy to bring you everything you could ever want to know about R600 caches.
The four texture units are connected to memory through two levels of cache. Unfiltered texture requests go through the Vertex Cache (which is unfiltered) and filtered requests make use of the L1 Texture Cache. Each of these caches is 32kB read only. All texture units share these caches.
Both the L1 Texture Cache and the Vertex Cache are connected to an L2 cache that is 256kB. This is the largest cache on the chip, and will certainly handle quite a bit of data movement with the possibility of 8k x 8k texture sizes moving forward.
As for the shader hardware, the cache connected to the SIMD units is an 8 kB read / write cache. This cache is used to virtualize register space if necessary, export data to the stream out buffer (which can be done from any type of thread and can bypass the need to send data to the render back ends). This cache is also used to accelerate things like render to vertex buffer.
Most of R600's write caches are write-back caches, although we weren't given any specifics on which write caches are not write-back. The impression is that any unit that needs to write out over the memory bus is connected through a write cache that enables write combining to maximize bus utilization, write latency hiding, and short term reuse. We assume that the shader cache (what AMD calls the Memory Read/Write Cache) is also write-back.
The only thing we are really missing regarding caches is the information for Z/stencil cache and color cache connected off of the render back ends.
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GoatMonkey - Monday, May 14, 2007 - link
That's obviously BS. This IS their high end part, it just doesn't perform as well as nVidia's high end part, so it is priced accordingly.poohbear - Monday, May 14, 2007 - link
sweet review though! thanks for including all the important and pertinent cards in your roundup (the 8800gts 320mb inparticular). also love how neutral Anand is in their reviews, unlike some other sites.:pCreig - Monday, May 14, 2007 - link
The R600 is finally here. I'm sure the overall performance is not what AMD was hoping for. Nobody ever shoots to have their newest product be the 2nd best. But pricing it at $399 and including a very nice game bundle will make the HD 2900 XT a VERY worthwhile purchase. I also have the feeling that there is a significant amount of performance increase to be realized through future driver releases ala X1800XT.shady28 - Tuesday, May 15, 2007 - link
Nvidia has gone over the cliff on pricing.
I know of no one personally who has an 88xx series card. I know one who recently picked up an 8600 of some kind, that's it. I have the best GPU of anyone I know.
It's a real shame that there is so much focus on graphics cards that virtually no one buys. These are niche products folks - yet 'who is best' seems to be totally dependent on these niche products. That's patently ridiculous.
It's like saying, since IBM makes the fastest computers in the world (they do), they're the best and you should be buying IBM (or now, lenovo) laptops and desktops.
No one ever said that sort of thing because it's patently ridiculous. Why do people say it now for graphics cards? The fact that they do says a lot about the mentality of sites like AT.
DerekWilson - Tuesday, May 15, 2007 - link
We don't say what you are implying, and we are also very upset with some of NVIDIA's pricing (specifically the 8800 ultra)the 8800 gts 320mb is one of the best values for your money anywhere and isn't crazy expensive -- it's actually the card I'd recommend to anyone who cares about graphics in games and wants good quality and performance at 1600x1200.
I would never tell anyone to buy an 8600 gts because nvidia has the fastest high end card. In fact, in this article, I hope I made it clear that AMD has the opportunity to capitalize on the huge performance gap nvidia left between the 8600 and 8800 series ... If AMD builds a part that performs in this range is priced competitively, they'll have our recommendation in a flash.
Recommending parts based on value at each price or performance segment is something we take pride in and will always do, no matter who has the absolute fastest hardware out there.
The reason our focus was on AMD's fastest part is because they haven't given us any other hardware to test. We will absolutely be talking a lot and in much depth about midrange and budget hardware when AMD makes these parts available to us.
yacoub - Monday, May 14, 2007 - link
$400 is a lot of money. Not terribly long ago the highest end GPU available didn't cost more than $400. Now they hit $750 so you start to think $400 sounds cheap. It's really not. It's a heck of a lot of money for one piece of hardware. You can put together a 650i SLI rig with 2GB of DDR2 6400 and an E4400 for that much money. I know because I just did that. I kept my 7900GT from my old rig because I wanted to see how R600 did before purchasing an 8800GTS 640MB. Now that we've seen initial results I will wait to see how R600 does with more mature drivers and also wait to see the 640MB GTS price come down even more in the meantime.vijay333 - Monday, May 14, 2007 - link
http://www.randomhouse.com/wotd/index.pperl?date=1...">http://www.randomhouse.com/wotd/index.pperl?date=1..."the expression to call a spade a spade is thousands of years old and etymologically has nothing whatsoever to do with any racial sentiment."
yacoub - Monday, May 14, 2007 - link
Yes, a spade was a shovel long before muslims enslaved europeans to do hard labor in north africa and europeans enslaved africans to do hard labor in the 'new world'.vijay333 - Monday, May 14, 2007 - link
whoops...replied to the wrong one.rADo2 - Monday, May 14, 2007 - link
It is not 2nd best (after 8800ULTRA), not 3rd best (after 8800GTX), not 4th best (after 8800GTX-640), but 5th best (after 8800GTS-320), or even worse ;)Bad performance with AA turned on (everybody turns on AA), huge power consumption, late to the market.
A definitive failure.