ATI Radeon HD 2900 XT: Calling a Spade a Spade
by Derek Wilson on May 14, 2007 12:04 PM EST- Posted in
- GPUs
Memory and Data Movement
Internal cache bandwidth on the R600 is 180GB/sec, while the internal memory bus, a second generation Ring Bus that builds on the X1k series idea, is able to deliver 100GB/sec of throughput in either read or write capacity. Memory offers nearly 110GB/sec, and AMD has stated that the internal bus is well matched to this due to the fact that some external bandwidth is wasted on overhead. The bottom line here is that a whole of data can move very quickly into and out of this hardware.
As we mentioned, R600 sees a reincarnation of the Ring Bus which can now handle both read and write data (X1k could only handle reads on the Ring Bus while writes were run through a crossbar). An independent DMA controller manages a bus comprised of multiple ring stops. There is one ring stop per pair of memory channels, and each ring stop is connected to two others via a 256 bit wide connection. The ring bus is 1024 wires total and can move read and write data in either direction to follow the shortest path around the ring to or from the memory client or memory.
The Ring Bus allows the PCI Express bus to be treated like just another memory device by the rest of the hardware. The DMA hardware is able to manage all the traffic to and from onboard and system memory in the same manner, and the memory clients on the GPU don't need to know what device they're talking to. The Ring Bus services 84 read clients and 70 write clients.
The external memory interface is 512-bit, doubling the X1k maximum of 256-bit and surpassing G80's 384-bit memory bus. Memory speeds are lower than on previous generation high end AMD hardware, but total bandwidth is higher. The net result is that AMD only slightly edges out G80 for memory bandwidth.
In implementing the 512-bit memory interface, AMD didn't want to add any more I/O pads to its package. They accomplished this by making use of a stacked I/O pad design. Unfortunately, details were vague on the implementation and methods used to keep clock speed high in spite of the proximity of other high frequency I/O.
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johnsonx - Monday, May 14, 2007 - link
and to which are you going to admit to?What was that old saying about glass houses and throwing stones? Shouldn't throw them in one? Definitely shouldn't them if you ARE one!
Puddleglum - Monday, May 14, 2007 - link
You mean, while it does compete performance-wise?johnsonx - Monday, May 14, 2007 - link
No, I'm pretty sure they mean DOESN'T. That is, the card can't compete with a GTX, yet still uses more power.INTC - Monday, May 14, 2007 - link
Chadder007 - Monday, May 14, 2007 - link
When will we have the 2600's out in review?? Thats the card im waiting for.TA152H - Monday, May 14, 2007 - link
Derek,I like the fact you weren't mincing your words, except for a little on the last page, but I'll give you a perspective of why it might be a little better than some people will think.
There are some of us, and I am one, that will never buy NVIDIA. I bought one, had nothing but trouble with it, and have been buying ATI for 20 years. ATI has been around for so long, there is brand loyalty, and as long as they come out with something that is competent, we'll consider it against their other products without respect to NVIDIA. I'd rather give up the performance to work with something I'm a lot more comfortable with.
The power though is damning, I agree with you 100% on this. Any idea if these beasts are being made by AMD now, or still whoever ATI contracted out? AMD is typically really poor in their first iteration of a product on a process technology, but tend to improve quite a bit in succeeding ones. I wonder how much they'll push this product initially. It might be they just get it out to have it out, and the next one will be what is really a worthwhile product. That only makes sense, of course, if AMD is now manufacturing this product. I hope they are, they surely don't need to make anymore of their processors that aren't selling well.
One last thing I noticed is the 2400 Pro had no fan! It had a heatsink from Hell, but that will still make this a really attractive product for a growing market segment. Any chance of you guys doing a review on the best fanless cards?
DerekWilson - Wednesday, May 16, 2007 - link
TSMC is manufacturing the R600 GPUs, not AMD.AnnonymousCoward - Tuesday, May 15, 2007 - link
"I bought one, had nothing but trouble with it, and have been buying ATI for 20 years."That made me laugh. If one bad experience was all it took to stop you from using a computer component, you'd be left with a PS/2 keyboard at best.
"...to work with something I'm a lot more comfortable with."
Are you more comfortable having 4:3 resolutions stretched on a widescreen? Maybe you're also more comfortable with having crappier performance than nvidia has offered for the last 6 months and counting? This kind of brand loyalty is silly.
MadBoris - Monday, May 14, 2007 - link
As far as your brand loyalty, ATI doesn't exist anymore. Furthermore AMD executives will got the staff so you can't call it the same.Secondly, Nvidia has been a stellar company providing stellar products. Everyone has some ups and downs. Unfortunately with the hardware and drivers this is ATI's (er AMD's) downs.
This card should do ok in comparison to the GTS, especially as drivers mature. Some reviews show it doing better than GTS640 in most tests, so I am not sure where or how discrepencies are coming about. Maybe hardware compatibility, maybe settings.
rADo2 - Monday, May 14, 2007 - link
Many NVIDIA 8600GT/GTS cards do not have a fan, are available on the market now, and are (probably; different league) much more powerful than 2400 ;) But as you are a fanboy, you are not interested, right?