The Makings Of Radeon HD 5850
Radeon HD 5850 centers on a different PCB than its big brother. That’s good news, since we were already a little concerned about the 5870’s 11” length. The 5850 is a much more accommodating 9.5,” making it smaller than the Radeon HD 4870 X2.
To that end, the Radeon HD 5850 doesn’t sport the two top-mounted six-pin auxiliary power connectors we’ve come to appreciate on Nvidia’s cards. Rather, it reverts back to a pair of rear-mounted six-pin plugs, like the Radeon HD 4870. This is less-favorable, we think, because it extends the clearance needed behind your graphics card by at least another inch or two, depending on the rigidity of those cables.
Aside from the shorter board and power connectors, the only other aesthetic difference between the Radeon HD 5870 and 5850 is that the Radeon HD 5850’s backside isn’t covered. Fortunately, video cards have no shame.
This means the same implementation of Eyefinity enabled through the Radeon HD 5870 carries over here as well. Two dual-link DVI outputs, an HDMI connector, and a DisplayPort can be mixed and matched for any combination of three digital outputs, as long as one of the three outputs is DisplayPort (thanks to reader Bounty for pointing this out). Otherwise, you're limited to two DVI outputs or one DVI/HDMI output. And for those who read the original review and thought something wonky was up with our bitstreaming testing—it was, and here’s photographic proof.
Fortunately, CyberLink is going to pick up the Onkyo receiver we use to test and work on compatibility before PowerDVD 9 is formally patched to support this functionality. No word yet on TotalMedia Theatre or WinDVD incorporating support for AMD’s 5800-series.
Under The Hood
| Header Cell - Column 0 | Radeon HD 5870 | Radeon HD 5850 | Radeon HD 4870 |
|---|---|---|---|
| Die Size | 334 square millimeters | 334 square millimeters | 263 square millimeters |
| Transistors | 2.15 billion | 2.15 billion | .956 billion |
| Memory Bandwidth | 153 GB/s | 128 GB/s | 115 GB/s |
| AA Resolve | 128 | 128 | 64 |
| Z/Stencil | 128 | 128 | 64 |
| Texture Units | 80 | 72 | 40 |
| Shader (ALUs) | 1,600 | 1,440 | 800 |
| Idle Board Power | 27W | 27W | 90W |
| Active Board Power | 188W | 151W | 160W |
Once you get past the card’s looks, there are few other tweaks to the board’s vital specs that affect its performance. To begin, while the Cypress GPU driving AMD’s Radeon HD 5850 is the same as the one powering 5870, two of its SIMD arrays are disabled, turning off 160 of its shader processors and eight of its texture units. The chip's total consequently drops to 1,440 ALUs and 72 texture units. Its clock rate is also slowed from 850 MHz to 725 MHz.
Cypress’ back-end remains unchanged, with 32 ROPs and Z/stencil rates that are affected only by the GPU’s clock. As with the Radeon HD 5870, the 5850 boasts a 256-bit memory bus populated by 1GB of GDDR5. Of course, it’s running slower than the 5870, at 1 GHz rather than 1.2 GHz, yielding 128 GB/s of bandwidth instead of 153 GB/s. Even still, that’s still more than the Radeon HD 4870’s 115.2 GB/s.
ATI uses the same power-saving tweaks that helped Radeon HD 5870 dip in at 27W idle to do the same here. Same GPU, same idle clocks, same 27W floor. But because two of the processor’s 20 SIMD arrays are disabled, and because 3D clocks are lower, maximum board power drops to 151W—9W lower than a Radeon HD 4870, 37W lower than the 5870, and 19W lower than the spec ATI originally provided when the Radeon HD 5870 launched last week.
