Radeon HD 6790 review - The Barts LE Graphics processor

Posted by Hilbert Hagedoorn on: 04/04/2011 01:00 PM [ 0 comment(s) ]

The Barts LE Graphics processor

Right then, let's get started. If you read our Barts GPU reviews, the Radeon 6850 and 6870, then pretty much this is what is being used in the Radeon HD 6790, surprisingly enough.

AMD took that GPU, disabled some shader processor clusters and tags the GPU as Barts LE. Being Barts, it comes with the more popular VLIW5 architecture and it is based on 10 Streaming Multiprocessor units (out of the fourteen available), that gives the R6790 a good 800 shader processors.

AMD Radeon HD 6790 Process	40nm
Transistors	1.7B
Engine Clock	Up to 840 Mhz
Stream Processors	800
Compute Performance	Up to 1.34 TFLOPs
Texture Units	40
Texture Fillrate	33.6 GTexel/s
ROPs	16
Pixel Fillrate	13.4 GPixel/s
Z/Stencil	53.8 GSample/s
Memory Type	GDDR5
Memory Clock	Up to 1050 MHz
Memory Bus Width	256 bit
Memory Data Rate	Up to 4.2 Gbps
Memory Bandwidth	Up to 134.4 GB/s
Load Board Power	150W
Idle Board Power	19W

In pale comparison, the R6850 has 12 SM units and 960 stream processors (they call the GPU the Barts PRO). A cool fact about the R6790 is that AMD did not fiddle with the memory bus. Typically when products go cheaper, they cut the memory bus in order to allow for cheaper memory to be used. The R6790 has the full 256-bit bus and it's memory is clocked in at an effective data-rate of 4200 MHz, that will give them 134.4 GB/s of graphics memory bandwidth.

The GPU clocks in at 840 MHz and the GPU is expected to have TDP of just under 150W, and will draw power from two 6-pin power connectors. That TDP is a little on the high-side we feel, especially compared to what we really measure ... which is just 105W.

Let's have a quick comparative overview of some of the specifications representing a certain cope of mid-range performance products

Specifications	Radeon HD 5770	Radeon HD 6790	Radeon HD 6850	Radeon HD 6870
GPU	Juniper XT	Barts LE	Barts Pro	Barts XT
Manufact. tech.	40nm	40 nm	40nm	40nm
GPU frequency	850 MHz	840 MHz	775 MHz	900 MHz
Stream processors	800	800	960	1120
Memory frequency	4800 MHz	4200 MHz	4000 MHz	4200 MHz
Memory bus	128-bit	256-bit	256-bit	256-bit
Memory buffer	1 GB GDDR5	1 GB GDDR5	1 GB GDDR5	1 GB GDDR5
Power consumption	108 watt	150 watt	~ 127 watt	>150 watt

So we now have three BARTS based SKUs, the two R6800 SKUs each have a separate codename: the R6850 being Barts Pro and the 6870 being the Barts XT. The R6790 being Barts LE.

We'll leave the entire codename thing for what it is now and move a little onward into the architecture.

All cards are of course updated DX11 class product with a couple of new features. Armed with 1.7 billion transistors the Radeon HD 6790 is pitted against the competition's GeForce GTX 550 Ti model.

The product has 10 SIMD clusters, 40 texture units, 800 shader processors, 16 ROPs and a TDP of 150W, 19W in idle. Despite the memory bus you can recognize similarities close to the R5770 here. This product however will bring you 1.34 TFLOPS of performance, and combined with that 256-bit gDDR5 memory, it will leave the R5770 far behind it.

AMD Radeon HD 6970

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