RV730 Architecture

Unlike RV635, RV730 is based on an entirely new GPU design that’s derived from ATI’s RV770 GPU architecture found in the Radeon 4850 and 4870. With prices on Radeon 4600 cards starting at just $69 though, the emphasis on RV730 was to make it cheaper for ATI to produce than RV770.

To accomplish this ATI has dramatically reduced the number of shading units inside RV730. While RV770 boasts up to 800 stream processors, just 320 stream processors are found within RV730. Interestingly enough, this is the same number of shaders found in ATI’s previous high-end architecture, RV670/R600.

As a result there are cases where the Radeon 4670 comes awfully close to matching the performance of Radeon 3850, if not outperforming it, but more on this later.

In comparison to RV770, ATI has adjusted the arrangement of the SIMD cores. RV730 ships with half the number of stream processors per SIMD core, just 40 shaders in RV730 per SIMD core versus 80 shaders per core in RV770. RV730 boasts 8 SIMD cores total, resulting in a grand total of 320 stream processors (40 stream processors per SIMD core x 8 SIMD cores). Like RV770, each SIMD core in RV730 has four dedicated texture units bringing the total number of texture units to 32 inside RV730.

If you recall, texturing was a huge shortcoming in ATI’s previous generation architecture. RV670 supported just 16 texture units. So RV730 has two times the number of texture units as ATI’s previous generation high-end architecture, and four times the number of texture units as its direct predecessor, the Radeon 3650. Like RV770, RV730’s texture units have also been redesigned to deliver up to two times the texture cache bandwidth of RV670.

The ROP subsystem has been improved as well. RV730 sports 8 ROPs. That’s two times the number of ROPs as RV635. ATI has also tweaked the ROPs to provide double the AA fill-rate for 32-bit and 64-bit color as well as double the peak rate for depth/stencil operations. These improvements allow the RV730 to perform quite competitively with the Radeon 3850 despite its memory bandwidth disadvantage: 32GB/sec in Radeon 4670 versus 57.6GB/sec in the 3850.

Speaking of the memory interface, we should mention that like other mainstream card offerings it’s 128-bit wide, so no change there in comparison to RV635. However, ATI clocks the memory on the Radeon 4670 up to 1.0GHz (2.0GHz effective), yielding 32GB/sec of peak memory bandwidth. The Radeon 3650 topped out at 25.6GB/sec.

RV730 continues to rely on TSMC’s 55-nm manufacturing process, with the chip containing approximately 514 million transistors. Each RV730 chip sports a die size of just 146 square millimeters with a max TDP of 59W for the Radeon 4670, and 48W for the Radeon 4650.

RV730 SKUs

As we just mentioned, ATI will be offering two different GPUs based off RV730: the Radeon 4670 and the Radeon 4650. Digging deeper, ATI will be offering multiple 4670 and 4650 configurations, with memory sizes ranging from 512MB of GDDR3 graphics memory up to 1GB of DDR3 for the 4670, while 512MB and 1GB SKUs for the 4650 will also be provided. The following chart summarizes ATI’s 4600 series lineup:

Radeon 4600 Comparison
	Radeon 4670 512MB	Radeon 4670 1GB	Radeon 4650 512MB
# of Stream Processors	320	320	320
Core Clock	750MHz	750MHz	600MHz
Memory Interface	128-bit	128-bit	128-bit
Memory Clock	1000MHz	900MHz	500MHz
Memory Type	GDDR3	DDR3	DDR2
Memory Bandwidth	32GB/sec	28.8GB/sec	16GB/sec
Texture fill-rate	24 Gigatexels/sec	24 Gigatexels/sec	19.2Gigatexels/sec
MSRP	$79	NA	$69
Max Board Power	59W	59W	48W

As you can see, ATI will be shipping the 4670 with GDDR3 and conventional DDR3 memory types. We’ve been told that latency between the two memory types should be the same, however AMD uses GDDR3 on the 512MB model because it supports 8-bit burst and also 1GHz DDR3 modules are more expensive. Instead ATI relies on 900MHz DDR3 for their 1GB Radeon 4670 boards.