AMD Radeon HD 7770 £100

15th Feb 2012 | 05:01

AMD Radeon HD 7770

Southern Islands architecture with a friendly price tag

TechRadar rating:

3.5 stars

Like:

Powers off when your system's idle; Offers bleeding-edge tech for less; Beats the GTX 550 Ti for performance...

Dislike:

...but not AMD's own HD 6850

Overview

AMD showed its hand first in this year's GPU arms race with Nvidia... by turning it into last year's arms race.

While Nvidia has kept shtum about its upcoming new 'Kepler' architecture and looks to do so until Spring, AMD stole the march and released the first of its new 7-series cards, the AMD HD 7970, a few days before Christmas 2011.

That sure was odd timing, but it taught us a lot about AMD's new Southern Islands architecture, specifically the 'Tahiti' chip. It's fully PCIe 3.0-supported, uses a 28nm manufacturing process to pack more transistors onto a PCB than ever before, and apart from offering very quick DX11 game frame rates, it's a highly energy efficient beast.

When your system drifts off into standby, the Tahiti card switches itself all but off too, minimising power draw.

The HD 7970's whopping £440 price made all those neat features all but irrelevant to the gaming masses though, so we're putting our hopes on this HD 7770 to deliver the best bits of the new AMD architecture for a more palatable price.

The 'Cape Verde' chip that this HD 7770 is built around makes full use of the new Graphics Core Next architecture like its big bro, with ZeroCore power efficiency in tow and a solid 1,000 MHz core clock. If it can offer a slice of the HD 7970's performance for this price, it's on to a winner.

Architecture, technology and specifications

HD 7770

The Graphics Core Next architecture is a bold move from AMD in that it represents a move away from the VLIW instruction used in 6-series cards towards a GPU-processing-friendly SIMD vector processor.

The previous processor type was great for graphics processing, but not suited to general purpose GPU computing - AMD left that side of things up to Nvidia and its CUDA cores.

Graphics Core Next is a u-turn on that philosophy though. GCN allows up to 16 data elements to be processed in a single clock cycle.

Grouping data before it runs through the vector processor is really efficient when dealing with general processing tasks - but the bad news for games is that you won't notice that difference in Battlefield 3 - the strengths of this architecture are wider-reaching than that, even as far as the professional market.

GCN also understands advanced languages like C++, meaning that in the long run, it'll be easier for developers to make use of the 7-series cards for complex programs.

The performance improvement from this architecture comes from passing data through a ton of compute units, which all work on the same operation until it's completed, and the resulting compute performance of this HD 7770 card is impressive at 1.28 TFLOPS.

It's built with ten compute units rather than the HD 7970's sixteen, but that's still enough to demonstrate a marked performance increase on last generation's equivalent model. And with AMD and Nvidia now adopting similar stances in their design, it's becoming an increasingly straight battle between the two - no hiding behind the blurred lines of CUDA cores and stream processors.

So the number of compute units and the simplified SIMD instructions they perform give AMD's 7-series cards the brains, but the clock speed is still the brawn of the operation. And at a world-first 1,000 MHz, it's fair to say the HD 7770 has brawn in check.

Benchmarks

HD 7770

We tested the HD 7770 with the most demanding DX11 around at 1080p, and with the Heaven 2.5 benchmark at 2560 x 1600 to really test its limits. It fared reasonably, demonstrating why it's more expensive than the HD 7750 and keeping in the same ball park as the pricier but older HD 6850.

DirectX 11 tessellation performance: Frames per second: Higher is betterHeaven 2.5

AMD HD 7770: 11.9
AMD HD 6850: 12.5
EVGA GTX 550 Ti: 8.9

DirectX 11 gaming performance: Frames per second: Higher is better

DiRT 3

AMD HD 7770: 41.73
AMD HD 7750: 28.64
AMD HD 6850: 42.62

Shogun 2

AMD HD 7770: 30.77
AMD HD 7750: 20.33
AMD HD 6850: 31.86

Metro 2033

AMD HD 7770: 13.00
AMD HD 7750: 11.67
AMD HD 6850: 15.67

Just Cause 2

AMD HD 7770: 31.18
AMD HD 7750: 26.13
AMD HD 6850: 34.14

Verdict

HD 7770

Many of the HD 7770's new features won't be noticeable right away. The underlying architecture is a big step forward for AMD that programmers and developers will find attractive, but for gamers looking to get playable frame rates out of DX11 games at 1080p its benefits aren't as obvious.

We're expecting the HD 7770 to enter at around the £100 point, which means it's going up against Nvidia's 550 Ti. While we didn't see it outperform the Nvidia card by the 100% AMD implied, it does hold a clear performance advantage, in addition to the subtler features under its bonnet.

Our sticking point though is that it was outclassed in every benchmark we ran by the previous generations' darling; the HD 6850. With just £20 difference between the two cards, we'd have liked to have seen a closer battle between the two.

It's worth mentioning that AMD's drivers tend to get better results from any given card after a few months of refinement, so further down the line we might see more parity in the benchmark figures between the two cards.

As with the HD 7750, the HD 7770 didn't impress in its overclocking performance the way AMD's high-end HD 7970 did. That £440 card maxed out AMD's overclocking software settings before crashing; the same can't be said here.

We managed to add on another 50 MHz to the core and memory clocks which yielded a modest increase in our benchmark tests, but it wasn't a reliable runner with those settings - glitches and crashes kicked in after a few minutes. Hopefully we'll see the full extent of the HD 7770's potential when the third party manufacturers release their beefed-up versions.

The 7-series might not all deliver staggering performance and overclocking, and that's to be expected given their wildly different pricings, but there is one feature that consistently impresses across the range - ZeroCore.

This is power-efficiency taken to a happy extreme – when your system enters a long-idle state, the HD 7700 along with all 7-series cards completely powers down the fan, 3D engine, compute units, shaders – virtually the whole card. The only activity going on comes from a small bus control block, which simply lets your computer know that the card still exists and no-one stole the GPU while it's been asleep.

We found it to be fast-acting, and dramatically reduced power draw when our system went idle.

We liked

This HD 7770 brings AMD's new architectural features to the budget audience with reasonable success.

Its GCN design and ZeroCore power efficiency make it a compelling argument to choose new over old, but it doesn't quite blow the best of the 6-series cards out of the water in plain old gaming performance.

We disliked

The HD 6850 can't do the 7-series cards' tricks, but it can render Metro 2033 frames quicker, and that makes the HD 7770 a tricky one to recommend.

As a stock card, it doesn't offer anything outstanding, but aftermarket companies might yet yield some impressive performances out of it.

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graphics cards Radeon Graphics Core Next Southern Islands AMD
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