Radeon HD 4770s In CrossFire
So how much graphics muscle are you really getting for $220, and how does that compare to the competing single-GPU solutions?
Two Radeon HD 4770s give you 1,280 total shader processors, two 512 MB GDDR5 frame buffers (each on a 128-bit bus), 32 total ROPs and the ability to filter up to 64 textured pixels per clock. Each board in the CrossFire configuration runs a 750 MHz core clock and memory at 800 MHz—effectively 3,200 MT/s.
Why is CrossFire so gosh-darned viable right now? For several generations of chipsets dating back to the 955X Express, Intel platforms have supported the multi-card rendering technology. AMD chipsets dating back to the Radeon Xpress 200 also extend support. So, there’s a huge install base of core logic and motherboards that are compatible.
In contrast, Nvidia has historically limited its SLI technology to Nvidia’s own AMD-/Intel-based chipsets. It was only recently made available on another vendor’s platform via licensing (Intel’s X58). Clearly, Nvidia is realizing that a protectionist policy isn’t the way to go. In fact, we even heard of one motherboard vendor whose budget X58 boards originally didn’t support SLI, were BIOS-hacked to enable it, and then worked-through with Nvidia on a proper implementation—all without having to pay for the license!
How about the oft-mentioned (by Nvidia) concern that, because ATI doesn’t have as close a relationship with game developers—specifically those involved in its TWIMTBP program—that CrossFire is riddled with compatibility issues? There’s actually some validity to such a worry, especially if you enjoy picking up games as soon as they're released. We've seen titles, such as FEAR 2, where CrossFire compatibility is specifically listed as a known issue. Fallout 3 with quad-GPU CrossFire can also be problematic, according to ATI's own Catalyst release notes.
At the same time, none of the games in our test suite gave us trouble. CrossFire isn’t perfect, but after seeing what a pair of 4770s can do slung together, you’ll want to reconsider your reservations.
| Header Cell - Column 0 | Radeon HD 4890 | Radeon HD 4870 | Radeon HD 4770 CrossFire | GeForce GTX 280 | GeForce GTX 260 C216 |
|---|---|---|---|---|---|
| Manufacturing Process | 55 nm TSMC | 55 nm TSMC | 40 nm TSMC | 65 nm TSMC | 55 / 65 nm TSMC |
| SPs | 800 | 800 | 640 x 2 | 240 | 216 |
| Core Clock | 850 MHz | 750 MHz | 750 MHz | 602 MHz | 576 MHz |
| Shader Clock | 850 MHz | 750 MHz | 750 MHz | 1,296 MHz | 1,242 MHz |
| Memory Clock | 975 MHz GDDR5 | 900 MHz GDDR5 | 800 MHz GDDR5 | 1,107 MHz GDDR3 | 999 MHz GDDR3 |
| Frame Buffer | 1 GB | 1 GB / 512 MB | 512 MB x 2 | 1 GB | 896 MB |
| Memory Bus Width | 256-bit | 256-bit | 128-bit x 2 | 512-bit | 448-bit |
| ROPs | 16 | 16 | 16 x 2 | 32 | 28 |
| Price | ~$250 | ~$190 | ~$220 | ~$310 | ~$180 |
Power And Heat
The Radeon HD 4770 earned praise for its 40 nm technology and resulting cut in power consumption. Indeed, it uses the least power at idle and under load of any other graphics card we tested here.
But what happens when you add a second board in CrossFire? As expected, power consumption jumps significantly. At idle, the two 4770s use more power than any of the single-GPU solutions. Under load, however, the 40 nm RV740 retains its advantage and ducks in under the Radeon HD 4890 and Radeon HD 4870 1 GB cards, using more power than the GeForce GTX 260 Core 216.
If you were looking for more information on the 40 nm process’ effect on GPU temperature, here you go. These were all measured through GPU-z after 10 minutes of idle and then a series of looped 1920x1200 Crysis runs in a window.
You can see that a lone Radeon HD 4770 is the coolest of ATI’s cards at both idle and under full load. Interestingly enough, though, each board required a slightly different fan speed in order to achieve its temperatures. We'll see if these results correspond to overclocking in just a bit.
