AMD Radeon HD 6790 Review: More Mid-Range Might

Hot on the heels of Nvidia's GeForce GTX 550 Ti introduction, AMD releases a card with the same £115 MSRP and vastly superior performance. But can it also stand up to the GeForce GTX 460 768 MB? We put the new card to the test!

Today, AMD introduces its new Radeon HD 6790, a card designed to fill space between the Radeon HD 5770 and Radeon HD 6850. As such, this board's natural competition is Nvidia's GeForce GTX 460 768 MB.

The funny thing is, Nvidia recently announced that the GeForce GTX 460 768 MB is about to be discontinued. GeForce GTX 550 Ti arrived only a few weeks ago, designated as its replacement in the space between the GeForce GTS 450 and GeForce GTX 460 1 GB.

A New Card And Familiar GPU

Before we go any further, let’s have a closer look at the Radeon HD 6790’s GPU, designated Barts LE:

This graphics processor is built using a cut-down RV870 (Barts) ASIC first seen during the Radeon HD 6800-series launch. Fully featured, this graphics processor has 14 SIMD engines, each with four texture units and 16 stream processors. Each stream processor, in turn, hosts five ALUs (AMD refers to these as stream cores). 

In the Radeon HD 6790, four of the SIMD engines are disabled, resulting in a total of 40 texture units and 800 stream cores. When it comes to pixel output, the Radeon HD 6790 uses two of Barts’ four render back-ends, each containing eight full-colour ROP units, adding up to 16 total. Those of you familiar with the Radeon HD 5770 may notice that this card shares the exact same number of stream cores, texture units, and ROPs.

From here, however, things get interesting. Four 64-bit memory controllers yield an aggregate 256-bit memory interface. This is unchanged from the Radeon HD 6800-series, and is twice as potent as the 128-bit memory interface on the Radeon HD 5770. Moreover, the Radeon HD 6790 sports an 840 MHz core and 1050 MHz GDDR5 memory. Once again, this is very close to the Radeon HD 5770’s 850 MHz core and 1200 MHz memory frequencies.

With all of this info in hand, it seems clear that AMD's aim with the Radeon HD 6790 was to create a Radeon HD 5770 with a 256-bit memory interface. Of course, being based on the newer Barts architecture, this card has all of the feature benefits of the Radeon HD 6800-series, including improved tessellation performance, Eyefinity enhancements, and the ability to accelerate Blu-ray 3D video over HDMI.

With these facts in mind, let’s compare the Radeon HD 6790 to the rest of the playing field:

The Radeon HD 6790's 256-bit interface demonstrates a huge memory bandwidth advantage over the Radeon HD 5770. This should manifest itself in a number of situations—most notably, when anti-aliasing is enabled. Indeed, if it weren't for the removal of half of its ROPs, the Radeon HD 6790 would be very close competitor to the Radeon HD 6850.

We know it will perform better than Radeon HD 5770, and not as fast as the Radeon HD 6850. But how will it compare to its GeForce competition?

Since the GeForce GTX 550 Ti performs similarly to the Radeon HD 5770, we expect the new Radeon HD 6790 to easily and challenge the GeForce GTX 460 768 MB. It’s interesting that both of these cards are cut-down versions of higher-end models, but crippled in somewhat different ways. The GeForce GTX 460 768 MB has the same shader core, texture unit, and clock specifications of Nvidia's 1 GB card, but with one-third fewer ROPs and a narrower memory bus. On the other hand, the Radeon HD 6790 has fewer shader cores and texture units compared to the Radeon HD 6850. But it runs at higher clocks to compensate. The main difference is that the number of ROPs are halved, from 32 to 16.

In any case, the GeForce GTX 460 768 MB offers much more interesting competition for AMD’s new card. We anticipate the benchmarks will go back and forth between these two products, depending on the game.