The Radeon HD 4850 & 4870: AMD Wins at $199 and $299
by Anand Lal Shimpi & Derek Wilson on June 25, 2008 12:00 AM EST- Posted in
- GPUs
One, er, Hub to Rule them All?
With R500 AMD introduced its first ring bus, a high speed, high bandwidth bus designed to move tons of data between consumers of memory bandwidth and the memory controllers themselves. The R600 GPU saw an updated version of the ring bus, capable of moving 100GB/s of data internally:
On R600 the ring bus consisted of two 512-bit links for true bi-directional operation (data could be sent either way along the bus) and delivered a total of 100GB/s of internal bandwidth. The ring bus was a monster and it was something that AMD was incredibly proud of, however in the quest for better performance per watt, AMD had to rid itself of the ring and replace it with a more conventional switched hub architecture:
With the ring bus data needed to be forwarded from one ring stop to the next and all clients got access to the full bandwidth, regardless of whether or not they needed it. For relatively low bandwidth data (e.g. UVD2 and display controller data), the ring bus was a horrible waste of power.
With the RV770 all that exists is a simple switched hub, which means that sending data to the display controller, PCIe and UVD2 (AMD's video decode engine) traffic are now far less costly from a power standpoint. Another side effect of ditching the ring bus is a reduction in latency since data is sent point to point rather than around a ring. With the move to a hub, AMD increased their internal bus width to 2kbits wide (which is huge). Maximum bandwidth has increased to 192GB/s (in 4870) but this depends on clock speeds.
With nearly double the internal bandwidth and a point to point communication system, latency between memory clients should be decreased, and huge amounts of data can move between parts of the chip. Certainly getting enough data on to the GPU to feed 800 execution units is a major undertaking and AMD needed to make a lot of things wider to accommodate this.
The CrossFire Sideport
Although AMD isn't talking about it now, the CrossFire Sideport is a new feature of the RV770 architecture that isn't in use on the RV770 at all. In future, single-card, multi-GPU solutions (*cough* R700) this interface will be used to communicate between adjacent GPUs - in theory allowing for better scaling with CrossFire. We'll be able to test this shortly as AMD is quickly readying its dual-GPU RV770 card under the R700 codename.
One thing is for sure, anything AMD can do to assist in providing more reliable consistent scaling with CrossFire will go a long way to help them move past some of the road blocks they currently have with respect to competing in the high end space. We're excited to see if this really makes a difference, as currently CrossFire is performed the same way it always has been: by combining the output of the rendered framebuffer of two cards. Adding some sort of real GPU-to-GPU communication might help sort out some of their issues.
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shadowteam - Wednesday, June 25, 2008 - link
Did you know these chips can do up to 125C? 90C is so common for ATI cards, I haven't had one since 2005 that didn't blow me hair dry. Your NV card was just a bad chip I suppose. Why do you think NV or ATI would spend a billion dollars in research work, then let its product burn away due to some crappy cooling? They won't give you more cooling than you actually need. It's the same very cards that go to places like Abu-Dhabi, where room temps. easily hit 50C+.soloman02 - Wednesday, June 25, 2008 - link
Sorry, but no human would survive a temp of 50C.http://en.wikipedia.org/wiki/Thermoregulation#Hot">http://en.wikipedia.org/wiki/Thermoregulation#Hot
In fact the highest temp a human has survived was recorded by the Guinness book of world records as: 46.5C (115.7F). Keep in mind that was the internal temp of the guy. The temp on that day was 32.2C (90F).
http://www.powells.com/biblio?show=0553587129&...">http://www.powells.com/biblio?show=0553587129&...
http://www.time.com/time/magazine/article/0,9171,9...">http://www.time.com/time/magazine/article/0,9171,9...
If it is 50C in those rooms, the people inside are dead or dying.
The cards are probably fine. All it takes is to search google to back up your figures (or to disprove them like I just did).
shadowteam - Wednesday, June 25, 2008 - link
You're just a dumb pissed off loser. There's a big difference in internal human temperature to its surroundings. In places like Sahara, temperatures routinely hit 45C, and max out @ 55C. But does that mean people living there just die? No they don't, because they drink a lot of water, which helps their bodies get rid of excess heat so to keep their internals at normal temperature (32C). You didn't have this knowledge to share so you decided to Google it instead, and make fool out of yourself. Here, let me break it down for you,You said: "Keep in mind that was the internal temp of the guy"
Exactly, the guy was sick, and when you're sick, your body temperature rises, in which case 46C is the limit of survival. I suggest you take Bio-chemistry in college to learn more about human body, which is another 4 years before you finish school.
Ilmarin - Wednesday, June 25, 2008 - link
I'm not talking about chips failing altogether... just stability issues, similar to what you experience from over-zealous overclocking. Lots of people have encountered artifacting/crashes with stock-cooled cards over the years. If these are just 'bad chips' that are experiencing stability issues at high temps, then there are a lot of them getting through quality control. Of course NV and ATI do enough to make most people happy... but many of us have good reason to be nervous about temperature. I think they can and should do better. Dual slot exhaust coolers should be mandatory for the enthusiast/performance cards, with full fan control capability. Often it's up to the partners to get that right, and often it doesn't happen for at least a couple of months.shadowteam - Wednesday, June 25, 2008 - link
I think it's more profitable for board partners to just roll out a stock card rather than go through the trouble of investing time/money into performance cooling. What I've seen thus far, and it's quite apparent, that newer companies tend to go exotic cooling to get themselves heard. Once they're in the game, it's back to stock cooling. For example, Palit and ECS came up with nice coolers for its 9600s. Remember Leadtek from past years? They don't even do custom coolers any more. ASUS, Powercolor, Gigabyte, Sapphire etc just find it easier to throw in a 3rd party cooler from ZM, TT TR, and call it a day.DerekWilson - Wednesday, June 25, 2008 - link
you know we actually received an updated bios for a certain vendors 4850 that speeds the fan up a bit and should reduce heat ...i suspect a lot of vendors will start adjusting their fan tables actually ...
shadowteam - Wednesday, June 25, 2008 - link
I think this reply was meant for the guy right above me. I'm all for stock cooling :).ImmortalZ - Wednesday, June 25, 2008 - link
"Quake Wars once again shows the 4870 outperforming the GTX 280, but this time it offers essentially the same performance as the GTX 280 - but at half the price. "You mean the 260 in the first instance?
No text in The Witcher page. I assume this is intentional.
Also, I've heard on the web that the 48xx series has dual-link only on one of it's DVI ports. Is this true?
Oh and another thing - why is the post comment page titled "Untitled Page"? :P
rahat5810 - Wednesday, June 25, 2008 - link
Nice cards and nice article. But I would like to point out that there are some mistakes in the article, nothing fatal though. Like, not mentioning 4870 in the list of cards, writing 280 instead of 260, clicking on the picture to enlarge not working for some of the figures.feelingshorter - Wednesday, June 25, 2008 - link
AMD almost has a perfect card but the fact that the 4870 idles at 46.1 more watts than the 260 means the card will heat up people's room. At load, the difference of 16.1 watts more for the 4870 is forgivable.If its possible to overclock a card using software (without going into BIOS screen), then why isn't it possible to underclock a card also using software when the card's full potential isn't being used? I'd really be interested in knowing the answer, or maybe someone just hasn't asked the question?
I hardly care about Crysis, its more a matter of will it run Starcraft II with 600 units on the map without overheating. Why doesn't anandtech also test how hot the 4870 runs? Although the 4850 numbers aren't pretty at all, the 4870 is a dual slot cooler and might give better numbers right? I only want to know because, like a lot of readers, i have doubts as to whether a card like the 4850 can run super hot and not die within 1+ years of hardcore gaming.