A Closer Look At The Radeon 4830
It’s pretty common knowledge by now that the Radeon HD 4870 and Radeon HD 4850 are both based on the RV770 graphics processor. We’ve dug into the Radeon 4800 series architecture in Fedy Abi-Chahla’s review AMD Radeon HD 4850: Smarter by Design? , so we won’t go into the guts of the RV770. But to refresh your memory, the RV770 chip offers 800 stream processors, 40 texture units, and 16 raster operator units paired to a 256-bit memory bus. Both the Radeon HD 4870 and 4850 models feature the same graphics processor, while the faster 4870 model offers higher clock speeds and faster GDDR5 memory compared to its 4850 sibling.
However, the new Radeon 4830 is a little different. Its graphics processor is called the RV770 LE. But it’s not really a new part--it’s the same 55 nm R770 GPU, but with some of its functionality turned off. Instead of 800 stream processors, the RV770LE offers 640 stream processors. Instead of 40 texture units, the RV770 LE offers 32. Thankfully, AMD left all of the 16 raster operator units functional in the RV770 LE, so the GPU retains some of its original prowess.
Everything else has been untouched, so all of the features offered in the Radeon HD 4870 and 4850 remain in the 4830: its Unified Video Decoder 2. 0, HDMI 7. 1 audio over HDMI, DirectX 10. 1, Shader Model 4. 1, CrossFireX compatibility, and PCI Express (PCIe) 2. 0 signaling support. Let’s look at a chart to better illustrate the differences between the 4800 models:
|Radeon 4800 Series Comparison|
|Card:||Radeon 4830||Radeon 4850||Radeon 4870|
|Process:||55 nm||55 nm||55 nm|
|Core Speed MHz:||575||625||750|
|Memory Speed MHz:||900 (1, 800 DDR)||993 (1, 986 DDR)||900 (3, 600 DDR5)|
|DirectX /Shader Model:||DX 10. 1 /SM 4. 1||DX 10. 1 /SM 4. 1||DX 10. 1 /SM 4. 1|
As we can see, while the clock speeds of the new 4830 most closely resemble those of the 4850, the newer card still has a 50 MHz core and a 93 MHz memory speed deficit. With fewer stream processors paired with lower clock speeds, the Radeon HD 4830 will probably need quite a bit of overclocking to reach the performance of its bigger brother. On the plus side, the R770 was designed for higher clock speeds in mind, so the RV770 will likely have quite a bit of overclocking overhead.
Let’s also have a quick look at a comparison between the specs of the new 4830 and its arch-nemesis, the GeForce 8800 GT/9800 GT:
|Radeon 4830/GeForce 9800 GT comparison|
|Card:||Radeon 4830||GeForce 8800 GT/9800 GT|
|Core Speed MHz:||575||600|
|Memory Speed MHz:||900 (1, 800 DDR)||900 (1, 800 DDR)|
|DirectX /Shader model:||DX 10. 1 /SM 4. 1||DX 10. 0 /SM 4. 0|
Because the G92 is a little older, it’s made with the 65 nm process compared to the 4830’s 55 nm process. This might give the 4830 an edge when it comes to power usage, keeping the temperatures lower, and when overclocking.
When we look at the number of stream processors, the 4830 appears to have five times the power of the 8800 GT. This is extremely misleading, as the 8800 GT and 4830 architectures couldn’t be more different. We do know that the 128 stream processors in the GeForce 9800 GTX+ allow that card to perform roughly equivalent to the 800 stream processor-equipped Radeon 4850. With this in mind, the 8800 GT and Radeon 4830 should definitely be in the same ballpark as far as shader power is concerned. On the flip side, the 8800 GT looks to have almost twice the texture units of the 4830. But once again, the two cards have such wildly different architectures that this likely won’t manifest itself in a colossal advantage. Everything else looks identical: 16 raster operator units, a 256-bit memory bus, and 900 MHz GDDR3 memory are specifications both cards share.
It’s very important to note that in this review we benchmarked the Radeon HD 4830 not against a reference 8800/9800 GT, but against the factory-overclocked Gigabyte 8800 GT TurboForce edition. This particular card has a full 100 MHz graphics processor overclock to 700 MHz compared to the stock 600 MHz speed, and a 20 MHz memory overclock to 920 MHz compared to the stock 900 MHz speed. We use this card because there are a lot of overclocked 9800 GT cards out there at the 4830’s price point, so we wanted to paint a worst-case scenario for the new 4830.
Now that we have a good idea of what the Radeon HD 4830 is all about and how it sizes up against the competition, let’s scrutinize some of the flavors being offered by PowerColor and Sapphire.