Radeon HD 5570 Architecture
In the conclusion of the Radeon HD 5670 review I wrote last month, I mentioned that I hoped the Radeon 5500-series would include a DDR3-based version of the Radeon HD 5670. It looks like it's my lucky day:
| Header Cell - Column 0 | Radeon HD 5570 | Radeon HD 5670 |
|---|---|---|
| Shader Processors: | 400 | 400 |
| Texture Units: | 20 | 20 |
| Color ROPs: | 8 | 8 |
| Core Clock: | 650 MHz | 775 MHz |
| Memory Clock: | 900 MHz (DDR3) | 1,000 MHz (GDDR5) |
| Memory Bus: | 128-bit | 128-bit |
| Data Rate: | 1.8 Gb/s | 4 Gb/s |
| Transistors (Millions): | 627 | 627 |
Yes, the new Radeon HD 5570 is a DDR3-equippped Radeon HD 5670 with a 125 MHz-lower core clock rate. If you look at the data rate, you can see that the Radeon HD 5570 offers less than half the memory bandwidth of the 5670. This is because DDR3 theoretically delivers half of the bandwidth that GDDR5 memory provides at the same clock speed and on the same memory bus. As a result, we can expect a significant difference in performance between these two closely-related cards.
Here's a look at the GPU block diagram:
The Radeon HD 5570 GPU, like the Radeon HD 5670, contains five SIMD engines, each with four texture units and 16 stream processors. Of course, each stream processor sports its five ALUs (ATI calls them Stream Cores). As a result, this GPU boasts 400 total stream cores and 20 texture units. Note that there are two 64-bit memory controllers sharing two render back-ends. Each render back-end contains four color ROP units, resulting in a total of the eight specified ROPs and a 128-bit memory interface.
Lets compare this to the Radeon HD 4670, which the 5570 will likely be replacing:
| Header Cell - Column 0 | Radeon HD 5570 | Radeon HD 4670 |
|---|---|---|
| Shader Processors: | 400 | 320 |
| Texture Units: | 20 | 32 |
| Color ROPs: | 8 | 8 |
| Fabrication process: | 40nm | 55nm |
| Core Clock: | 650 MHz | 750 MHz |
| Memory Clock: | 900 MHz | 1000 MHz |
| Memory Bus: | 128-bit | 128-bit |
| Data Rate: | 1.8 Gb/s | 2 Gb/s |
| Transistors (Millions): | 627 | 514 |
At first glance, the 5570 looks impressive because of its shader processor increase. But when we dig a little deeper, we can start to see some chinks in the new card's armor. The older Radeon HD 4670 has a 100 MHz core clock speed advantage over the new 5570, and this almost makes up for the 5570's higher shader core count. The older 4670 also includes more texture units and a higher reference memory clock. Granted, it has been our experience that most of the Radeon HD 4670s in the wild actually come equipped with an 800 MHz clock speed (200 MHz under reference). But, from the reference specifications alone, we expect the Radeon HD 5570 to serve as a somewhat-parallel move from the 4670.
At this point, we're really not surprised. The sub-$100 Radeon HD 5000-series cards are not here to raise the bar with regard to game performance. Instead, they offer roughly similar 3D alacrity at any given price, but with the value-adds inherent to the product family: DirectX 11 support, Eyefinity, bitstreaming Dolby TrueHD and DTS-HD Master Audio, and ATI Stream. This is good news if you were upgrading from integrated graphics, and less so if you're already rocking a Radeon HD 4000-series card.