ATI Radeon HD 4870 X2

Verdict:

[+] CrossFire
Extremely fast in most of our test games

[-] Missfire
Hot; power hungry

ATI has always been clear about its strategy regarding the HD 4800-series – it would initially launch the single-GPU HD 4850 and HD 4870 cards, and then release a dual-GPU card to address the ultra-high performance end of the market. This dual-GPU card is the ATI Radeon HD 4870 X2.

The name sounds familiar since it follows the same naming scheme as the Radeon HD 3870 X2 but we hoped that this new card wouldn't be as frustrating. While the 3870 X2 boasted average frame rates were much better than a HD 3870, we found the minimum frame rates we experienced in games were typically lower than single GPU cards in most titles, making for a more stuttery, unsatisfying gaming experience than with the cheaper, single-GPU HD 3870. ATI has had time to develop its drivers and hardware since the HD 3870 X2, however.

HARDWARE UPDATES

First off, the HD 4870 X2 card has a phenomenal 2GB of GDDR5 memory on board, clocked at 1.8GHz (3.6GHz effective) which is split equally between the two GPUs. This is in contrast to the GPU of a Radeon HD 4870 which only links to 512MB of 1.8GHz GDDR5 memory. The GPUs of the HD 4870 X2 are pretty much the same as that of HD 4870 in other respects – like those on the single card, each of the two chips on the new X2 has 800 stream processors (making for 1,600 in total) and the GPUs run at 750MHz, for example.

That said, there is one new inclusion with the GPUs of the HD 4870 X2, as this diagram shows (opens in new window). The new inclusion is called 'Sideport' and it's a method for the GPUs on the 4870 X2 to directly communicate with each other.

ATI confirmed that Sideport is currently disabled but it can be switched on in a later driver. ATI gave mixed messages as to exactly what Sideport is or how it works, but claimed it could give extra performance as and when it’s enabled. As Sideport is currently disabled, there’s no way of testing it.

As you can see from the slide, ATI has also upgraded the PCI-E bridge chip that accepts data from the main system and buses it to and from the two GPUs. On the HD 3870 X2 the bridge chip was only PCI-E 1.1, and thus restricted to 2.5GB/sec of bandwidth.

The new PCI-E 2.0 bridge chip can send 5GB/sec along its data paths. This is noteworthy as ATI has previously stated that the PCI-E 1.1 bridge chip of the HD 3870 X2 was sufficient for the types of work it had to do.

Also interesting is ATI’s claimed peak power draw of the HD 4870 X2, which is only 286W. This seems odd given that a single HD 4870 card draws 160W (so you'd assume that two HD 4870s in CrossFire would consume 320W in total) and that the HD 48760 X2 card has an extra 1GB of RAM to power plus the PCI-E 2.0 bridge chip. That the HD 4870 X2 only has one PCB to the two of the CrossFire setup could account for the lower than expected power draw.

The 286W power draw means that the HD 4870 X2 has one 6-pin PCI-E power connector and one 8-pin PCI-E power connector. The card is 10.5in long and has a dual-slot cooler.

CINEMATIC GAMING

Before we wanted to share two impressive tech demos that ATI had sent us. They both fit ATI's current ambition of making game visuals look as good as movies. The first clip is from the forthcoming Ruby demo, while the second is from famed director David Fincher and production company Anonymous Content. We were only sent videos rather than the demos themselves, and ATI didn't confirm what system was used to create these scenes. Still, they're incredibly good looking - although we've got streaming copies running in this webpage, we recommend you download the high-res versions of the videos to see just how impressive these videos are.

* Click here download the Ruby demo (50MB)

* Click here download the Fincher demo (52MB)

HOW WE TESTED

We compared the HD 4870X2 with a single Radeon HD4870 and two HD 4870’s in CrossFire using a BETA Catalyst driver from AMD for the HD 4870 X2 and the new Catalyst 8.7 package with the HD 4870 and the pair of HD 4870s. We will also compare results with a GeForce GTX 280 as ATI has told us it will price the HD 4870 X2 at US$549 (roughly £290 ex VAT). Even though some GTX 280 cards now cost as little as £265 inc VAT, this is Nvidia's most comparable single product.

Nvidia is due to release a new ForceWare 177.83 driver on 12 August for the GT 200 series, but unfortunately we didn't have time to retest with this driver. The company also says that a pair of GTX 260s in SLI is the most comparitive Nvidia offering to test against, but again this information arrived too late for testing.

PERFORMANCE

Click here for the benchmark graphs (opens in new window)

Crysis in short was finally playable on a ATI graphics card at 1,920 x 1,200 with 4x AA - the HD 4870 X2 maintained a 26fps minimum frame rate and an average frame rate of 36fps on our test rig. A single HD 4870 can only manage a minimum frame rate of 11fps - less than half that of the HD 4870 X2 - with an average frame rate of 23fps. Two HD 4870s in CrossFire performed less than admirably, only managing a minimum frame rate of 15fps and average frame rate of 33fps at 1,920 x 1,200.

The HD 4870 X2 is also a touch faster than a GeForce GTX 280: both cards run Crysis at a minimum of 26fps at 1,920 x 1,200, but the HD 4870 X2 has the superior average of 36fps rather than 31fps.

The HD 4870 X2 performed very similarly at a lower resolution of 1,680 x 1,050 with 2x AA, with a minimum frame rate of 27fps and an average of 36fps. You’d normally expect a card to perform much better at lower resolutions, so either our test rig's overclocked 3.33GHz Core 2 Extreme QX6850 overclocked is limiting the speed of the HD 4870 X2, or there's more power to be had from the card with future driver updates.

The 1,680 x 1,050 resolution in Crysis does seem a tricky one for ATI however, as the GTX 280 proved faster than the HD 4870 X2, with an average frame rate of 39fps and a minimum of 33fps.

Race Driver: Grid saw the HD 4870 X2 matched by the pair of HD 4870s in CrossFire; unsurprisingly, the single HD 4870 lagged far behind. At 1,920 x 1,200 for example, the HD 4870 X2 managed a minimum frame rate of 107fps and the two HD 4870s in CrossFire didn’t drop below 106fps. Average frame rates were also identical, with a HD 4870 X2 scoring 130fps to the 131fps of the pair of HD 4870s in CrossFire. A single HD 4870 achieves a minimum of 61fps and an average of 80fps at 1,920 x 1,200.

Both these minimum frame rates put the GTX 280 in the shade as it only managed a minimum of 64fps and an average of 77fps at 1,920 x 1,200, which is 40 per cent slower than the HD 4870 X2 or the pair of HD 4870s in CrossFire (although of course, it's still far from tardy).

Call of Duty 4 usually works well with multi-GPU setups, but the benefits of the second GPU of the HD 4870 X2 at 1,920 x 1,200 weren’t as significant as in GRID or Crysis. A single HD 4870 managed a minimum frame rate of 41fps while both the HD 4870 X2 and two HD 4870s in CrossFire had only a slightly higher minimum frame rate of 49fps. This is still a touch faster than a GTX 280, which runs the game at a 40fps minimum.

Things are slightly different if you only look at the average frame rates, with a HD 4870 X2 and a pair of HD 4870s in CrossFire clearly faster than a single HD 4870. Both the multi-GPU configurations run CoD4 at an average of 107fps at 1,920 x 1,200 rather than the 83fps of a single HD 4870.

ArmA: Armed Assault was playable with a HD 4870 X2 at 1,680 x 1,050 with a minimum frame rate increasing of 27fps. A single HD 4870 can only manage a 20fps minimum at this resolution while two HD 4870s in CrossFire only produce a 23fps minimum at 1,680 x 1,050.

At 1,920 x 1,200 the results are a little peculiar. At this resolution a single HD 4870 is faster than both a HD 4870 X2 and two HD 4870’s in CrossFire - the HD 4870 X2 runs at a 18fps minimum, a pair of HD 4870s at a 20fps minimum and a single HD 4870 at a 21fps minimum. While none of the ATI hardware on test can run ArmA at 1,920 x 1,200, the GTX 280 can, with a minimum of 28fps and an average of 51fps.

While ATI might unlock extra performance with driver updates and enabling the Sideport technology of the HD 4870 X2, one thing is clear: right now, on day one, it's very fast and works well in our range of test games.

POWER CONSUMPTION

While gaming with the HD 4870 X2 our test PC drew 521W, while two HD4870’s drew 551W, so ATI's claims that the new card draws less than a pair of the older cards is correct. With a single HD 4870 installed our test PC drew up to 376W, while with a GTX 280 installed we saw the power draw rise to 422W. The HD 4870 X2 might be fast, but it's also power hungry.

We should also point out that the card creates a prodigious amount of heat - the air around the test PC was noticeably hotter than that of the rest of the CPC Labs after we'd finished testing. During testing we felt the need to point two case fans at the card, blowing across the rear and the large cooler. The metal plates on the rear of the HD 4870 X2 were painfully hot to touch even after relatively short periods of gaming, so don't think about cramming the HD 4870 X2 into a small, poorly cooled case.

FOLDING

A single HD 4870 scores 1783ppd while using Stanford's Folding@home GPU client and drew 349W while folding. Using a single instance of the folding client with the HD 4870 X2, only generated 1,237ppd while the system drew 334W. Clearly both cores weren't engaged and we couldn't, at the time of writing, convince an instance to run on each of the card's GPUs.

CONCLUSION

With its UK cost still unconfirmed, it's tricky to tell whether the HD 4870 X2 will be worth actually buying - expect a roundup of prices as and when the card launches and stock becomes available in shops. When we have a confirmed price, we'll be in a better position to give a definitive verdict on whether to make a purchase or not. Working with the MRSP of US$549 gives us, by current standards (i.e. Nvidia's vertiginous price drops) a pricey graphics card, though. Even if you do a straight price conversion and add VAT, you're looking at something in the region of £340 inc VAT, and of course, here in the UK it's never that simple. And there's nothing to say the card won't be more expensive than this in the first phase of its life.

There's no denying that ATI has really pulled out the stops to make the HD 4870 X2 competitive on performance though, which is a refreshing to change to the negativity surrounding the HD 3870 X2. The card is blisteringly fast in most of our test games, with only ArmA providing cause for concern. ArmA isn't very friendly to multi-GPU setups of any kind though, so this isn't surprising. What is surprising is the speed in Crysis, another game that typically doesn't like multi-GPU arrangements.

With performance in most games from the HD 4870 X2 comparable to that of two HD 4870s in CrossFire, it's hard to recommend a HD 4870 owner to buy a HD 4870 X2 rather than just another HD 4870 (unless their motherboard doesn't support CrossFire). Equally, if you haven't got a particularly large screen (one at least capable of 1,680 x 1,050 pixels, if not more) then the HD 4870 X2 is overkill. But if you want a very fast piece of hardware, a big screen and you have a case that can keep it cool, the Radeon HD 4870 X2 is the fastest graphics card going by a long way.

Sapphire 1GB HD 4850 X2	68%
Nvidia GeForce GTX 295	81%
Sapphire 1GB HD 4870 Toxic	81%
Sapphire HD 4870 Toxic	81%
Sapphire HD 4870 Toxic	0/6
ATI Radeon HD 4670	79%
BFG GeForce GTX 260 OCX MaxCore	79%

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