The 5970 Clock Speed Debate

Now that you’ve seen the Radeon 5970’s specs, you’re probably wondering why it isn’t clocked as high as the Radeon 5870. The answer is actually pretty simple: power consumption.

If you rewind back to our coverage of the Radeon 4890 launch, you’ll remember that we asked ATI about the potential of introducing a Radeon 4890 X2 card. At the time ATI told us that they could certainly produce a 4890 X2 card if demand was there, but they didn’t want to make such a card without the backing of OEMs and system vendors. ATI was apparently receiving some backlash against the amount of power such a card would generate; the 4890 X2 board’s TDP was pegged at over 300W.

After polling their partners, ATI ultimately couldn’t find enough interest to potentially introduce a Radeon 4890 X2.

Now enter the 5870. Its max board power is actually pretty comparable to the 4890 (190W for the 4890 vs 188W for the 5870), leaving ATI with the same dilemma all over again -- a dual-GPU 5870 card is going to draw over 300W of juice. The 5850 on the other hand consumes just 10W more power than the 4870, making it a more feasible platform for ATI to work with.

Citing the 4890 X2 project as an example, we brought this up with ATI during our phone briefing regarding the 5970. Did OEMs kill the full-speed 5870 X2 as well?

At one foot long the 5970 is considerably longer than 4870 X2

ATI was adamant that OEMs didn’t play the deciding role this time around. While OEMs feelings regarding a 300W+ board certainly were a concern, ATI says the primary reason why they decided not to opt for the full 5870 speeds and feeds for the 5970 was they wanted to maintain compatibility with the existing power supply infrastructure.

Quite simply, ATI didn’t want users to potentially have to upgrade their PSU (power supply unit) just to run the 5970. They wanted the card to be compatible with as wide a variety of PSUs as possible.

Therefore in order to make the card work with as wide a variety of PSUs as possible, while still retaining as much of the 5870’s performance, ATI opted to deliver a card with the full 1600 shaders as the 5870, but with the 5850’s clock speeds.

This move brought the card’s power consumption just under their 300W budget. 294W to be exact (in comparison, the 4870 X2’s TDP was 286W). As such, just two power connectors are needed. One 8-pin PCIe 2.0 connector, and one 6-pin PCIe connector.

Power connections on 5970

Ironically enough, while ATI was able to maintain PSU compatibility with the 5970, the board is completely out of bounds with regards to its size. The 5970 board measures 12” in length from end-to-end. If you remember the NVIDIA’s original Quad SLI board from 2006, the GeForce 7900 GX2, ATI’s Radeon 5970 is pretty similar in length.

It’s a little funny that ATI’s so adamant about maintaining PSU compatibility considering that the Radeon 5970 will probably require many users to purchase a new system case just to get the card to fit. Between the two issues, we personally think the size of the 5970 is the bigger obstacle: two 8-pin PCIe 2.0 connectors are capable of supplying up to 300W of juice to the card. That plus the 75W sent up the PCIe interface itself should be more than enough for a full-speed 5970 card. Most high-end PSUs that have shipped in the last two years are outfitted with multiple 8-pin and 6-pin PCIe connectors.

In comparison, you’re going to need a really large full-tower case to house the 5970. It extends nearly 3” beyond our Gigabyte EX58-Extreme motherboard. That’s right where the hard drive cage sits in most system cases. ATI will be offering a full list of compatible cases at http://game.amd.com/us-en/crossfirex_certification.aspx. You’ll want to keep a close eye on this list if you plan to run a Radeon 5970 board.

As we mentioned on the previous page, in some ways the Radeon 5970 is ATI’s first Black Edition GPU. We’ll explain why next…