ATI Radeon HD 4850 review

Ridiculously high expectations are an occupational hazard in the computer chip industry. So, it's not often that a new product exceeds them. But by doing just that AMD's new ATI Radeon HD 4800 series of graphics cards, officially launched today, marks itself out as something seriously special.

That's right, folks, the Radeon HD 4800 GPU, previously codenamed RV770, is unequivocally, undeniably, unmistakably excellent. In fact, it might just be the most efficient, effective and elegant graphics chip that the world has ever seen. It certainly delivers a bigger bang for your buck than any graphics chip before. And yet it is not quite the fastest.

Cheap chip, but no chump

To understand why RV770 is so good – and, incidentally, why it doesn't matter that it fails to pinch the outright performance crown back from arch rival NVIDIA – let's take a quick tour of the key specifications.

The big news is a boost in the number of shader cores compared with the existing Radeon HD 3800 series. Astonishingly, AMD has managed to nearly triple the shader count from 320 units to 800.

The 4800's texture-processing capabilities have also ballooned from 16 to 40 units. Factor in core clockspeeds that are approximately on a par with the 3800 Series and the result is monumental boost in raw processing power.

But don't get the idea that AMD has merely blown a massive transistor budget to simply cut 'n' paste more functionals units into the GPU core. This new pixel pounder may offer much the same DirectX 10.1 3D feature set as ye olde Radeon HD 3800.

It's even based on precisely the same 55nm silicon production technology. But what AMD has done is so much more sophisticated than create an oversized 3800 core.

Compact and cost effective

Every aspect of the chip has been overhauled and redesigned with an eye to both efficiency and performance. The result, is an extremely compact and cost-effective graphics chip.

To appreciate just how compact it is, try this for size. Despite the 150 per cent increase in shader and texture units, the 4800 Series has just 44% more transistors. It's also rather revealing to compare the 4800's raw computer power with that of NVIDIA's new mega-GPU, the GeForce GTX 280.

The fastest of the new Radeon HD 4800 boards, the 4870 (see below for full specifications), is capable of a colossal 1.2TFlops of raw compute power courtesy of 956 million transistors.

Now, that might sound like a lot of transistors. But the GeForce GTX 280 requires no less than 1.4 billion transistors in return for 0.933TFlops of processing power.

So, not only is the 4800 smaller and cheaper to make. It's also more power efficient. AMD reckons the maximum power consumption of the 4800 Series is 160 watts while the GTX 280 sucks up an enormous 236 watts.

GDDR5 arrives

Further highlights of the 4800 series include the introduction of a new graphics memory type for the 4870 model. With a data rate of 3.6GHz, the new GDDR5 chips are not far off twice as fast as the best previous graphics memory.

That's handy because the one area where the 4800 looks a little deficient is the width of its memory bus. At just 256 bits, it is half the width of the beastly GeForce GTX 280.

It's also a relief to note that AMD has reintroduced a conventional box-filter algorithm for anti-aliasing. With the launch of the Radeon HD 2900 series early in 2007, AMD introduced a new programmable or 'adaptive' approach to smoothing the jagged edges of rendered objects. In theory it was more sophisticated. In practice it was just plain slow.

For the record, AMD has also retained and improved adaptive AA for the 4800 series, so now you can have the best of both worlds.

Needless to say, the 4800 series supports AMD's Crossfire multi-GPU technology. With a suitable motherboard, you can combine up to four 4800 boards for what will theoretically be the most powerful real-time rendering rig in the consumer market.

Minor matter of performance

But what about the most important metric of any GPU's success, performance? At launch there are two Radeon HD 4800 models. The 4850 clocks in at 625MHz core and 2GHz memory and we reckon will sell for a startlingly low price of around £130.

The top chip will be the 4870 with core and memory clockspeeds of 750MHz and 3.6GHz respectively and should squeak in under £200. US prices for the two boards are $199 and $299. Both cards are equipped as standard with 512MB of graphics memory. However, some board makers will release larger 1GB cards shortly after launch – for a price, of course.

Our first hands-on with the 4800 Series takes the form of the cheaper 4850 board. It's actually quite tricky to choose a direct competitor, since the arrival of the 4800 will inevitably push prices of existing graphics chipsets from NVIDIA down.

Sizing up the competition

With that in mind we've lined up the GeForce 8800 GTS 512MB, a card that typically sells for slightly more than £130 right now but should be available shortly for about the same money as the 4850. Our triple whammy of game tests takes in an old favourite, Half-Life 2, one of the most popular recent shooters, Call Of Duty 4, and the GPU-killer that is Crysis.

In both Call Of Duty 4 and Half-Life 2, the 4850 gives the GeForce board a pretty good pasting. At really high resolution settings such as 2,560 x 1,600 in Call Of Duty, for instance, the 4850 cranks out a reasonably smooth 32 frames per second average. That is seriously impressive for a sub-£150 video card. The 8800 GTS 512MB manages just 24 frames per second at the same settings.

Likewise, the 4850 makes utter mincemeat of Half-Life 2. 48 frames per second at 2,560 x 1,600 with 4x anti-aliasing and 8x anisotropic filtering is a great result. So, make no mistake. You can run both of these titles absolutely maxed out in terms of quality settings at any resolution you like and still enjoy smooth, stutter-free gaming.

Predictably, that's not the case with Crysis. Such is the astonishing fidelity of Crysis' 3D engine, it will probably a few years yet before any single graphics card can handle it with ease. Still, the 4850 is much more adept at processing the intensive shader code that Crysis is soaked in than any previous AMD card.

Our only minor reservation is that the 4850's advantage is slightly slimmer in Crysis than other titles. That doesn't necessarily bode all that well for upcoming games that push the performance envelope.

General purpose GPU

The final piece of the performance puzzle is the 4800's performance in so-called general purpose GPU (or GPGPU) applications. Currently there are few if any non-3D consumer level applications that can take advantage of the massive parallel processing power of modern GPUs.

However, both AMD and NVIDIA reckon that several are just around the corner, including video encode and photo editing. The benefits of using a GPU for this type of processing are said to be spectacular – as much as 20 times faster than any current CPU.

We'll be looking at these applications in detail when they appear later this year. Suffice to say for now it will be intriguing to discover if the 4800's advantage in raw compute power over NVIDIA's monstrous GeForce GTX 280 translates into actual performance superiority.

It's a wrap

So, that it folks. The new Radeon HD 4800 comfortably has the measure of its closest competition. OK, it's not the most powerful GPU on the planet. That honour remains with NVIDIA's GeForce GTX 280. But at around £450, the GTX 280 costs over three times as much as the 4850. It's also over twice as expensive as the 4870, a board that we estimate will get within 75 per cent to 80 per cent of the GTX 280 in terms of performance.

With any luck, we'll be firing up a Radeon HD 4870 board later this week to complete the 4800 series performance picture. We'll also be comparing it with a new higher-clocked version of the GeForce 9800 GTX which NVIDIA has prepped in response as well as the GTX 280, just to put AMD's new wonder chip into context. The results will be fascinating.

Update: NVIDIA has announced that the new higher-clocked GeForce 9800 GTX+ will be priced just $30 more than the Radeon HD 4850 in the US. Assuming a similar UK price gap, it should provide NVIDIA with a reasonable foil for AMD's new wonderchip.

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Spec showdown

ATI RADEON HD 4850:

Crysis (high quality)
1,280 x 1,024 x0 x0: 41 fps

Call Of Duty 4
1,920 x 1,200 x4 x8: 45 fps
2,560 x 1,600 x4 x8: 32 fps

Half-Life 2
1,920 x 1,200 x4 x8: 77 fps
2,560 x 1,600 x4 x8: 48 fps

NVIDIA GeForce 8800 GTS 512MB

Crysis (high quality)
1,280 x 1,024 x0 x0: 37 fps

Call Of Duty 4
1,920 x 1,200 x4 x8: 37 fps
2,560 x 1,600 x4 x8: 24 fps

Half-Life 2
1,920 x 1,200 x4 x8: 66 fps
2,560 x 1,600 x4 x8: 42 fps