RV770: AMD ATI Radeon HD 4870 - RV770: The Architecture

By Edward Chester



  • Editors choice
RV770: AMD ATI Radeon HD 4870


Our Score:


As well as the difference in texturing configuration, the SFUs in nVidia's architecture only appear at this point whereas there is an SFU in each MSPU in ATI's architecture. So, for every SIMD you get 16 SFUs whereas as each SM only has two.

nVidia combines 10 TPCs to create the shader power of GT200

Moving out a further step, things look even more different. Whereas nVidia combines three SMs and adds texturing capabilities (eight per TPC) to create a Texture/Processing Cluster (TPC) then combines 10 of these. ATI on the other hand skips straight to adding 10 SIMD cores together. The result is RV770 ends up with 640 SPUs, 160 SFUs (remember these can also do everything the SPUs can), and 40 texture units whereas GT200 has 240 SPUs, 60 SFUs, and 80 texture units. In comparison, R600 and RV670 had four SIMDs, making for a total of 256 SPUs, 128 SFUs, and 16 texture units.

ATI uses 10 SIMDs to create the shader power of RV770

Now it only takes a brief glance at those numbers to realise that somewhere along the way nVidia and ATI's tactics have massively differing results as ATI doesn't even pretend the 800 (640 + 160) SPUs in RV770 come close to competing with the 240 on GT200. We already mentioned that ATIs SPUs can only work on one thread at a time, so in many ways the 800 total SPUs could be considered to only have the same processing power as 160 SPs, which does more closely reflect average real world performance figures.

However, it's not quite as simple as that. If software is written in such a way that it benefits from the extra processors in ATI's architecture then it will run considerably faster, if it isn't then it will be slower than nVidia's cards. The only real conclusion we can draw at the moment is that nVidia's simpler approach will likely give more consistent performance in the short term. If software developers begin to embrace more complicated routines than ATI's hardware could pull away in the long term.

The same is true when you consider RV770 vs GT200 for GPGPU applications. While RV770 has theoretically more compute power, at 1.2 TeraFLOPs compared to GT200s 933GigaFLOPs, it requires programs to be written in such a way that they take full advantage. Time, and future benchmarks, will tell which turns out to be the best method.

Varis Vitols

July 5, 2008, 2:51 pm

Yeah, it was about time!

Matthew Bunton

July 5, 2008, 5:43 pm

This is the best bang for buck right now, good to see the ATI cards fighting back. Though it is still too early to upgrade in my opinion.


July 6, 2008, 1:18 am

if ati get cuda... i will get this card from sapphire(it have 2 (4 pin to 6 pin conector)(my power suply just have one 6 pin conector) but only if it get cuda, because i like to play games but i also do some video editing and transcoding videos to my zune and it take like 4hrs to covert a dvd to h.264 in my conroe


July 6, 2008, 2:10 am

Your comment on the CoD4 results is incorrect. The HD 4870 beats the GTX 280 comfortably.

It simply fails to be the double card GX2.

Varis Vitols

July 6, 2008, 3:58 am

It depends on what u upgrade from...


July 6, 2008, 6:14 am

Probably not worth upgrading from a 8800GT to a 4850 but the 4870 looks like it could be a possibility. Hopefully ATi will have OpenCL to compete against CUDA but I'm not bothered by the lack of support for it.


July 7, 2008, 3:35 pm

anybody know the minimum power supply rating? looking to install in Dual-Xeon Dell workstation with 700w PSU??


July 7, 2008, 4:06 pm

My X1950XTX is looking a bit long in the tooth now. Getting that itchy upgrade feeling.


July 7, 2008, 9:08 pm


I wouldn't look at it like that, it completely depends on what else you're running in your system. At peak the card will draw 150 - 200W, if you've got that much headroom in your current supply then you'll be fine. Otherwise you may need to upgrade. Easy way to check is with a plug-in power consumption meter. They're only about 㿀.

What card are you upgrading from?


July 8, 2008, 12:18 am

Hmmm, thanks ED. The Dell manual's state GPU's upto 150W(supported) so I may be pushing it if you say it draws upto 200W. Upgrading Dell PSU's I don't think is that easy as your probably aware most components are besopke (got to love Dell).


July 8, 2008, 1:09 pm

Ah, that could be a bit of a problem. Dells are an absolute pig to work with.


July 14, 2008, 5:22 pm

^^ wrt the Dell PSU prob - not sure about the Xeon's, some of the midi-tower cases still have the same footprint as a regular PSU, but just proprietary gaps for the kettle lead... in which case you can buy a normal PSU and get out the metal cutters and drill... I've got "creative" with a few Optiplex's over the years... :o)


July 14, 2008, 5:24 pm

and thanks for the great review!!

As per DMN's comment, that X1950XTX-GDDR4 (me too!) is suddenly looking really long in the tooth :o)))


February 15, 2009, 7:58 pm

i have got to get me one of these...

Joseph Middleton

August 24, 2009, 3:43 pm

This Radeon 4870 by HIS... It's not mentioned how much on board memory it has...

512MB or 1GB?

comments powered by Disqus