...and then disaster struck.

Or at least that's how it felt. The past few weeks have been incredibly tumultuous, sleepless, and beyond interesting. It is as if AMD and NVIDIA just started pulling out hardware and throwing it at eachother while we stood in the middle getting pegged with graphics cards. And we weren't just hit with new architectures and unexpected die shrinks, but new drivers left and right.

First up was GT200, which appeared in the form of the GeForce GTX 280 and GeForce GTX 260. Of course, both of those can be paired or tri-ed (if you will), but with two cards requiring at least a 1200W PSU we're a bit worried of trying three. Then came the randomness that was the accidental launch of the Radeon HD 4850 (albeit with no architectural information) and only a couple hours later we first heard about the 9800 GTX+ which is a die shrunk higher clocked 9800 GTX that is now publicly announced and will be available in July.

And now we have the other thing we've been working on since we finished GT200: RV770 in all it's glory. This includes the 4850 whose performance we have already seen and the Radeon HD 4870: the teraflop card that falls further short of hitting its theoretical performance than NVIDIA did with GT200. But theoretical performance isn't reality, and nothing can be done if every instruction is a multiply-add or combination of a multiply-add and a multiply, so while marketing loves to trot out big numbers we quite prefer real-world testing with games people will actually play on this hardware.

But before we get to performance, and as usual, we will want to take as deep a look into this architecture as possible. We won't be able to go as deep with RV770 as we could with GT200, as we had access to a lot of information both from NVIDIA and from outside NVIDIA that allowed us to learn more about their architecture. At the same time, we still know barely anything about the real design of either NVIDIA or AMD's hardware as they prefer to hold their cards very close.

This won't work long term, however. As we push toward moving compute intensive applications to the GPU, developers will not just want -- they will need low level architectural information. It is impossible to properly optimize code for an architecture when you don't know exact details about timing, latency, cache sizes, register files, resource sharing, and the like. While, this generation, we have decidedly more information from NVIDIA on how to properly program their architecture, we still need more from both AMD and NVIDIA.

And Now, the Rest of the Story

Last week was a weird teaser - we gave you the goods, without explaining what they were.

By now you know that the Radeon HD 4850 is the best buy at $199, but today we're able to tell you much about its inner workings as well as introduce its faster, more expensive sibling: the Radeon HD 4870.

ATI Radeon HD 4870 ATI Radeon HD 4850 ATI Radeon HD 3870
Stream Processors 800 800 320
Texture Units 40 40 16
ROPs 16 16 16
Core Clock 750MHz 625MHz 775MHz+
Memory Clock 900MHz (3600MHz data rate) GDDR5 993MHz (1986MHz data rate) GDDR3 1125MHz (2250MHz data rate) GDDR4
Memory Bus Width 256-bit 256-bit 256-bit
Frame Buffer 512MB 512MB 512MB
Transistor Count 956M 956M 666M
Manufacturing Process TSMC 55nm TSMC 55nm TSMC 55nm
Price Point $299 $199 $199

Priced at $299 the Radeon HD 4870 is clocked 20% higher and has 81% more memory bandwidth than the Radeon HD 4850. The GPU clock speed improvement is simply due to better cooling as the 4870 ships with a two-slot cooler. The memory bandwidth improvement is due to the Radeon HD 4870 using GDDR5 memory instead of GDDR3 used on the 4850 (and GDDR4 for 3870); the result is a data rate equal to 4x the memory clock speed or 3.6Gbps. The Radeon HD 4870 and 4850 both use a 256-bit memory bus like the 3870 before it (as well as NVIDIA's competing GeForce 9800 GTX), but total memory bandwidth on the 4870 ends up being 115.2GB/s thanks to the use of GDDR5. Note that this is more memory bandwidth than the GeForce GTX 260 which has a much wider 448-bit memory bus, but uses GDDR3 devices.

NVIDIA GeForce GTX 280 NVIDIA GeForce GTX 260 NVIDIA GeForce 9800 GTX ATI Radeon HD 4870 ATI Radeon HD 4850 ATI Radeon HD 3870
Memory Size 1GB 896MB 512MB 512MB 512MB 512MB
Memory Technology GDDR3 GDDR3 GDDR3 GDDR5 GDDR3 GDDR4
Memory Bus Width 512-bit 448-bit 256-bit 256-bit 256-bit 256-bit
Memory Clock 1107MHz 999MHz 1100MHz 900MHz 993MHz 1125MHz
Memory Data Rate 2.2Gbps 2.0Gbps 2.22Gbps 3.6Gbps 1.99Gbps 2.25Gbps
Memory Bandwidth 141.7GB/s 111.9GB/s 70.4GB/s 115.2GB/s 63.6GB/s 72.0GB/s

The use of GDDR5 enabled AMD to deliver GeForce GTX 260 class memory bandwidth, but without the pin-count and expense of a 448-bit memory interface. GDDR5 actually implements a number of Rambus-like routing and signaling technologies while still remaining a parallel based memory technology, the result is something that appears to deliver tremendous bandwidth per pin in a reliable, high volume solution.

AMD most likely took a risk on bringing GDDR5 to market this early and we do expect NVIDIA to follow suit, AMD is simply enjoying the benefits of jumping on the GDDR5 bandwagon early and getting it right, at least it seems that way. It wouldn't be too far fetched to imagine a 55nm GT200 die shrink with a 256-bit GDDR5 memory interface, it should allow NVIDIA to drop the price down to the $300 level (at least for the GTX 260).

As we mentioned in our Radeon HD 4850 Preview, both the Radeon HD 4870 and 4850 now support 8-channel LPCM audio output over HDMI. AMD just sent over 8-channel LPCM drivers for the Radeon HD 4870 so we'll be testing this functionality shortly. As we mentioned in our 4850 preview:

"All of AMD's Radeon HD graphics cards have shipped with their own audio codec, but the Radeon HD 4800 series of cards finally adds support for 8-channel LPCM output over HDMI. This is a huge deal for HTPC enthusiasts because now you can output 8-channel audio over HDMI in a motherboard agnostic solution. We still don't have support for bitstreaming TrueHD/DTS-HD MA and most likely won't anytime this year from a GPU alone, but there are some other solutions in the works for 2008."

The Radeon HD 4870 is scheduled for widespread availability in early July, although AMD tells us that some cards are already in the channel. Given that the 4870 relies on a new memory technology, we aren't sure how confident we can be that it will be as widely available as the Radeon HD 4850 has been thus far. Keep an eye out but so far the 4850 has been shipping without any issues at $199 or below, so as long as AMD can get cards in retailers' hands we expect the 4870 to hit its $299 price point.

AMD's "Small-Die" Strategy
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  • DerekWilson - Wednesday, June 25, 2008 - link

    greater than 100% scaling is due to margin of error combination for both single card and dual card tests in the vast majority of cases.

    we also tested single card performance on an nvidia system and crossfire performance on an intel system, so the different computers will also add margin of error.

    two card solutions generally don't scale at greater than 100% except in extraordinarily odd situations (where rebalancing loads might help with scaling on both individual cards -- but that's odd and rare).
    Reply
  • Sind - Wednesday, June 25, 2008 - link

    Why no 260 and 280 SLI? Reply
  • ImmortalZ - Wednesday, June 25, 2008 - link

    Because, with that kind of money, one can an entire system with one 48xx :P

    Also, page 10 appears to be broken.
    Reply
  • Lifted - Wednesday, June 25, 2008 - link

    No 260 or 280 SLI in the benchmarks, but they included them in the power charts. Odd. Reply
  • Anand Lal Shimpi - Wednesday, June 25, 2008 - link

    The power data was simply taken from the GTX 280 review, we just added to the list.

    As for the GTX 280 SLI numbers, we didn't include them as it it's mostly out of the price range of the Radeon HD 4870 ($1300 vs. $600 for two 4870s). We can always go back and redo the graphs to include them if you guys would like, but in the interim I would suggest looking at the GTX review to get comparison numbers.

    Take care,
    Anand
    Reply
  • DerekWilson - Wednesday, June 25, 2008 - link

    we actually only have one GTX 260, so we can't test that Reply
  • Clauzii - Wednesday, June 25, 2008 - link

    Yes, and the click to enlarge doesn't work.
    And believe it or not, posting right now from a AT page that looks like 1994...!
    Reply
  • ImmortalZ - Wednesday, June 25, 2008 - link

    Insert a buy in there. Need edit! Reply
  • TonyB - Wednesday, June 25, 2008 - link

    but can it play crysis? Reply
  • StevoLincolnite - Wednesday, June 25, 2008 - link

    Of course it can, There are benchmarks isn't there?
    Seriously ANY Direct X 9 card can run Crysis, The Quality and Performance is a different matter.
    Reply

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