The Radeon HD 5670 Architecture
Thus far, AMD's Radeon HD 5000-series has demonstrated a predictable relationship between the high-performance models ending in the suffix '70,' each successively-lower model offering half of the stream processors of its more powerful cousin. The Radeon HD 5670 continues this trend:
| Header Cell - Column 0 | Radeon HD 5970 | Radeon HD 5870 | Radeon HD 5770 | Radeon HD 5670 |
|---|---|---|---|---|
| Shader Processors: | 3,200 | 1,600 | 800 | 400 |
| Texture Units: | 160 | 80 | 40 | 20 |
| Color ROPs: | 64 | 32 | 16 | 8 |
| Core Clock: | 725 MHz | 850 MHz | 850 MHz | 775 MHz |
| GDDR5 Memory Clock: | 1000 MHz | 1200 MHz | 1200 MHz | 1000 MHz |
| Memory Bus: | 256-bit | 256-bit | 128-bit | 128-bit |
| Data Rate: | 8 Gb/s | 9.6 Gb/s | 4.8 Gb/s | 4 Gb/s |
| Compute Power (TFLOPs): | 4.64 | 2.72 | 1.36 | 0.62 |
| Transistors (Billions): | 4.3 | 2.15 | 1.04 | 0.627 |
| Maximum Power: | 294W | 188W | 108W | 61W |
| Idle Power: | 42W | 27W | 18W | 14W |
What's interesting here is that the new Radeon HD 5670 offers similar memory bandwidth compared to the higher-end Radeon HD 5770. Both cards offer a 128-bit bus with GDDR5 memory on-board, resulting in memory performance that isn't all that different.
Let's look at the Radeon HD 5670 block diagram for a better idea of how it compares to its siblings:
We went through the Radeon HD 5000-series architecture in detail in our Radeon HD 5870 launch article, so I won't rehash the minutia. We will look at the differences in the Radeon HD 5670 though. In short, the 5670 is one quarter of a 5870. It contains five SIMD engines, each with four texture units and 16 stream processors, and each stream processor with its five ALUs (which ATI calls Stream Cores). As a result, this GPU boasts 400 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 eight ROPs and a 128-bit memory interface.
Lets compare this to the Radeon HD 4770 we're hoping the new Radeon HD 5670 will be able to compete with:
| Header Cell - Column 0 | Radeon HD 5670 | Radeon HD 4770 |
|---|---|---|
| Shader Processors: | 400 | 640 |
| Texture Units: | 20 | 32 |
| Color ROPs: | 8 | 16 |
| Core Clock: | 775 MHz | 750 MHz |
| GDDR5 Memory Clock: | 1,000 MHz | 800 MHz |
| Memory Bus: | 128-bit | 128-bit |
| Data Rate: | 4 Gb/s | 3.2 Gb/s |
| Transistors (Billions): | .627 | 0.826 |
Our hopes that the Radeon HD 5670 will meet Radeon HD 4770 performance are somewhat dashed to some extent. The Radeon HD 4770 has more than a 50% increase in ALUs and texture units compared to the new 5670, not to mention two times the ROPs. The only real advantage the 5670 can boast compared to its previous-generation predecessor is a bit more bandwidth, due to a higher memory speed. Based on this, we're going to predict that the Radeon HD 5670 will fall well short of the 4770 when it comes to 3D gaming, and will instead have to pick up the slack with its value-added features.
The Radeon HD 4850 and 4770 are on the verge of extinction, which will open up some breathing room for the new $100 card in ATI's own lineup. The demise of the respectable GeForce 9800 GT and GTS 250 is less certain with GF100 (Nvidia's next-gen graphics architecture) delayed.
Of course there are quite a few capabilities that the Radeon HD 5000-series cards are able to boast currently not offered by its competition. For example, this card doesn't require a dedicated power connector. Moreover, you get some of the extras covered in previous Radeon HD 5000-series introductions: DirectX 11, Eyefinity, and bitstreaming Dolby TrueHD and DTS-HD Master Audio formats. Let's talk about how these features work on the Radeon HD 5670.
