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AMD Radeon HD 6790 1GB Review

AMD Radeon HD 6790 1GB Review

Manufacturer AMD
UK price (as reviewed) MSRP £115 (inc VAT)
US price (as reviewed) MSRP $149 (ex tax)

If you possess a particularly good memory when it comes to all things tech, you may recall the release of the ATI Radeon HD 5830 1GB back in February 2010. It was based on the eponymously named Cypress LE architecture, a cut-down version of the full-size Radon HD 5870 1GB’s Cypress XT GPU, and served to help ATI make use of its GPUs that couldn’t make the grade for either of its high-end cards at the time. However, once the supply of low-grade GPUs dried up, so did the HD 5830 1GB; the Cypress LE seeming to stand for limited edition.

AMD Radeon HD 6790 1GB Review
Our HD 6790 1GB review sample came dressed in the same cooler as an HD 6870 1GB

AMD’s Radeon HD 6790 1GB follows in the HD 5830 1GB’s footsteps, but is based on a Barts LE GPU this time. It’s a further scaled-down version of the Barts architecture found in both the HD 6850 1GB and HD 6870 1GB.

A further two SIMD engines have been disabled in comparison to the HD 6850 1GB, leaving the 6790 1GB with 800 stream processors, in comparison to the HD 6850 1GB’s 960 and the HD 6870’s 1,120. The HD 6790 1GB’s has a respectable 840MHz core clock, though, in comparison to the HD 6850 1GB’s 775MHz.

The HD 6790 1GB’s memory speed isn’t too shabby either, with its 1GB of GDDR5 clocked at 1.05GHz (4.2GHz effective) and connected by a 256-bit memory interface. This means the HD 6790 actually has more memory bandwidth than the HD 6850 1GB; 134.4GB/sec compared with the 128GB/sec of the HD 6850 1GB, which should help the card a little at higher resolutions.

AMD Radeon HD 6790 1GB Review
Board partners have had free rein on PCB designs and coolers. Here are the cards from HIS (left) XFX (centre) and Sapphire (right)

However, the real area where AMD has taken the axe to the HD 6790 1GB’s GPU is its ROP count. Both the HD 6850 1GB and HD 6870 1GB have a full set of 32 ROPs, but the HD 6790 1GB sports just 16. The HD 6790’s GPU back-end has escaped the cuts, though, meaning it still sports the same pair of rasterisers and single tessellation unit as both HD 68xx-series cards.

As it’s effectively another rung down on the specification ladder from the HD 6850 1GB, it’s odd that AMD hasn’t chosen to name this card the HD 6830. Instead, it's created a whole new 67xx range just for this card; cue never-ending tongue twisters involving the HD 6790 and HD 6970.

AMD Radeon HD 6790 1GB Review
All HD 6790 1GB cards will require two 6-pin PCI-E power connectors

Despite the nomenclature gymnastics, in reality the HD 6790 1GB will be placed in the middle of the £30 price gap between the £99 HD 5770 1GB and the £135 HD 6850 1GB, taking on Nvidia’s recently released GTX 550Ti 1GB.

As was the case with the HD 5830 1GB, there’ll be no stock model for the HD 6790 1GB, with board partners instead given free rein to use their own custom PCBs and coolers. While this means there should be plenty of competition and variety, it means our review sample, based on a stock HD 6870 1GB PCB, is only representative of graphics performance. Differences in cooling, power delivery circuitry and PCB design mean each partner’s card could perform very differently when it comes to thermal and acoustic performance.

One feature all partners cards will share, though, is the use of two 6-pin PCI-E power connectors, despite the fact that this card sits below the single 6-pin PCI-E powered HD 6850 1GB in AMD’s range. While part of this will be due to the HD 6790 1GB running at slightly higher clock speeds, the lower stream processor count should realistically negate this. We suspect that the extra power is required to keep the lower grade Barts LE GPU stable; our HD 6790 1GB reported a vcore of 1.175V, compared with the 1.094V of an HD 6850 1GB.

 AMD Radeon HD 6790 1GBAMD Radeon HD 6850 1GBAMD Radeon HD 5770 1GBNvidia GeForce GTX 550Ti 1GBNvidia GeForce GTX 460 1GB
GPU
CodenameBarts LEBarts ProJuniper XTGF116GF104
Frequency840MHz775MHz850MHz900MHz675MHz
Stream Processors800 (840MHz)960 (775MHz)800 (850MHz)192 (1,800MHz)336 (1,350MHz)
Layout10 SIMD Engines12 SIMD Engines10 SIMD Engines4 SMs, 1 GPC7 SMs, 2 GPCs
Rasterisers22212
Tessellation Units11147
Texture Units4048402856
ROPs1632162424
Transistors1.7bn1.7bn1.04bn1.17bn1.95bn
Size255mm2255mm2166mm2238mm2348mm2
Process40nm40nm40nm40nm40nm
Memory
Amount1GB GDDR51GB GDDR51GB GDDR51GB GDDR51GB GDDR5
Frequency1.05GHz (4.2GHz effective)1GHz (4GHz effective)1.2GHz (4.8GHz effective)1,026MHz (4,104MHz effective)900MHz (3.6GHz effective)
Interface256-bit256-bit128-bit192-bit256-bit
Bandwidth134.4GB/sec128GB/sec76.8GB/sec98.5GB/sec115GB/sec
Card Specifications
Power Connectors2 x 6-pin PCI-E2 x 6-pin PCI-E1 x 6-pin PCI-E1 x 6-pin PCI-E2 x 6-pin PCI-E
Maximum Power Draw150W127W108W116W160W
Idle Power Draw19W19WNot SpecifiedNot SpecifiedNot Specified
Recommended PSUNot SpecifiedNot Specified450W400W450W
Typical Street Price£115£135£100£115£135