Review: AMD Radeon HD 7950

Overview

AMD is really putting the pressure on Nvidia now with its second release of the new AMD HD 7000 graphics card generation, the AMD Radeon HD 7950.

Nvidia is still sitting back waiting for the right moment to strike back, but can it recover from these two quick blows?

Well, we say quick - it's been well over a month since AMD launched its first card of this generation, the AMD Radeon HD 7970.

That was a surprise given that, pre-Christmas, we were expecting both cards to hit the streets at the same time in the first week of January with a possible dual-GPU iteration coming around now.

AMD though decided to give its top-of-the-line, £500 AMD HD 7000 card a bit of breathing space at the start of its life, and now that the AMD Radeon HD 7950 is sat here in our labs it's easy to see why its release was delayed.

Essentially it's almost as good a card for over £100 less.

So AMD's claims to be delaying so it could wait for AMD Radeon HD 7950 units to be in the market (despite launching its big brother, the AMD Radeon HD 7970 well before you could even lay eyes on one) seem to be rather thin.

We think it's more likely AMD realised even fewer people would pick up a £500 graphics card when there was one for £350 that could do the same job practically as well.

To be fair though this isn't the first time this has happened; the previous generation had exactly the same problem in the two top-end Cayman cards – the Radeon HD 6950 and Radeon HD 6970.

There was precious little difference between the two cards in benchmarking terms, and with some judicious use of BIOS tweakery and ROM flashing fun, there ended up being precious little difference between them architecturally too.

But there must be some differentiating factors, some reason for the £150 price difference.

So, what has AMD chopped out of the AMD Radeon HD 7950 Graphics Core Next GPU to make the grade?

Architecture

The AMD Radeon HD 7950 is still based on the exact same Graphics Core Next/Southern Islands architecture as its only other AMD HD 7000 sibling, the HD 7970.

That means it's a graphics card still nailing the very latest of technologies in its rather sizeable package.

It's a fully fledged DirectX 11.1 card (though that's not actually going to be around soon, or even that big of a deal), more of interest though is the production process, shrinking down from the 40nm of the Cayman GPU to 28nm.

That's smaller than the current crop of CPUs.

That also means it can pack in a hell of a lot of those teeny transistors into the GPU, and AMD hasn't stinted. It's thrown 4.3 billion of them into this Tahiti core.

But it is a slightly chopped version of the Tahiti XT powering the AMD Radeon HD 7970.

This Tahiti Pro comes with only 28 of the Compute Units that make up the new vector processor AMD is now using for its graphics cards.

That means it's only rocking 1,792 shaders/Radeon Cores/streaming processors, or whatever you want to call them. Compared to the 2,048 of the Tahiti XT core that's a bit of a drop.

It also loses out on some 16 texture units, but thankfully it's still got the same full complement of ROPs at 32.

Outside of the GPU itself, the card as a whole comes with the same huge 3GB of GDDR5 frame buffer, on the same 384-bit interface.

And all still on the burgeoning PCIe 3.0 technology.

The clocks have also, inevitably, been cut back too.

The stock HD 7950 comes out of the box at 800MHz, a very conservative setting compared to the 925MHz of the HD 7970.

So, the AMD Radeon HD 7950 is not actually missing out on too much of AMD's new tech, indeed it's still hitting over 3TFLOPs of processing power to the HD 7970's 3.8TFLOPs.

For gamers though, forget FLOPs, it's polygon-pushing performance in games that we really want to know about. So how does that 20% drop in raw processing power translate into gaming benchmarks?

Benchmarks

At stock speeds the difference between the AMD Radeon HD 7950 and HD 7970 is actually quite pronounced, sometimes by as much as 25%.

That's a pretty reasonable performance difference between your top two GPUs, but it's not actually much to do with what's been chopped out of the GPU architecturally, more to do with the drop in clockspeed.

Once things are evened out in the core clock, through overclocking, there is suddenly almost nothing between the two AMD HD 7000 series cards.

The CrossFire performance is impressive for the AMD Radeon HD 7950 too, offering similar frame rates to the pricier cards, and the savings over the HD 7970 are multiplied in multi-GPU arrays.

DirectX 11 tessellation performance

DirectX 11 gaming performance

DirectX 10 gaming performance

Overclocking performance

CrossFire performance

Performance

As with any graphics card release it's all about performance and the AMD HD 7950 has got it in spades, and with a fair amount in reserve too.

At stock speeds the pace the AMD HD 7970 sets is tough for the HD 7950 to follow, leaving it at least 10% slower than its big brother. Sometimes that gap widens leaving the HD 7950 around 20% behind.

That's something that we would normally expect between the top two cards of a manufacturer's new generation.

But what of our assurances the AMD Radeon HD 7950 was almost as good a card?

Well as soon as you start waving around that familiar overclocking stick you can quickly see much of the difference between the two cards was taken up with the separation in core clockspeed.

Of course there's no guarantee that every Tahiti Pro GPU will be capable of these feats of overclocking, but the yields of these chips are only going to improve so I wouldn't be in the least surprised to see every Tahiti Pro capable of topping the 1GHz mark.

Like the HD 7970 before it we were able to drop into AMD's Overdrive software and push all the clock and memory sliders to their maximum settings without a problem.

In the case of the AMD Radeon HD 7950 that meant we hit 1,100MHz on the core and 1,575MHz for the memory.

That's fast.

And, as you can see from the benchmarks on the previous page, when the clockspeeds are pushed to the same limits there is almost nothing between the two top AMD HD 7000 series cards.

Considering the HD 7950 is over £100 cheaper than the HD 7970, that's quite impressive.

Interestingly though you don't even need to overclock the cards to make that difference disappear in CrossFire.

When the HD 7000 series cards are paired up there is again very little to separate them in terms of performance, and nothing that couldn't be closed if you just pushed the HD 7950 up to 925MHz.

Verdict

It's almost a shame AMD released the HD 7970 first when it could have had an instant hit, and a lot of good feeling over a month ago with the AMD Radeon HD 7950.

Though obviously people wouldn't have been quite so inclined to spend out for a HD 7970 when the cheaper card was just as capable a pixel-pusher.

But still, none of that can take away from the fact that the AMD Radeon HD 7950 is an excellent graphics card.

It's not just the AMD in-fighting that places this card at the top of the current crop of graphics cards.

We've been pushing the Nvidia GeForce GTX 580 as the go-to gamer's card since it was released, but the HD 7950 has that beat and for a good chunk of cash less than the Nvidia card.

And that's just at stock speeds. When you start overclocking this card the difference in performance increases hugely.

Even if you've never overclocked a graphics card in your life you owe it to all the engineers who worked on the Tahiti GPU to push it north of the 1GHz mark.

The reference cooler design, with its vapour chamber technology, is easily capable of absorbing the extra heat so the chance of causing any damage in doing so is negligible.

And all you need to do is bring up the AMD driver panel and push a couple of sliders.

Job done, instant, awesome frame rates.

Inevitably there are a host of factory overclocked Radeon HD 7950s on their way, like the Sapphire Radeon HD 7950 OverClock Edition, which will allow you to push the GPU even further.

The AMD HD 7950 could also be a massive hit for the CrossFire crew too, as for £700 you'll find yourself with an insanely quick graphics setup.

And for £300 less than an equivalent HD 7970 array.

Speaking of CrossFire too, it's worth mentioning that, like its big brother, the HD 7950 comes with the impressive AMD ZeroCore power tech.

That means if you've got a pair of GPUs running in your machine they'll only both be drawing power when you run a game. In normal desktop mode the second GPU switches off entirely, reducing power draw and unnecessary fan noise.

The primary GPU will also shut itself off almost entirely when the rig's screen goes into standby too.

For such power hungry gaming rigs these power saving functions are vital, and very, very welcome.

So AMD has got itself a real winner here with the HD 7950, even if it will inevitably cannibalise the sales of the pricier HD 7970.

We liked

The stock performance of the HD 7950 is impressive, but it's the amount of head-room for overclocking that Tahiti Pro core represents which really makes this card.

The ZeroCore Power tech is another of our favourite things about the HD 7950. Realistically you'll never notice it in action, but it will be there, saving you money unobtrusively in the background.

We disliked

The only thing to dislike about the card is the fact the clockspeed has been set so artificially low. Thankfully though AMD hasn't locked the overclocking possibilities down as it did with the HD 6950.

We did try flashing the BIOS of our reference HD 7950 to see if we could re-enact the fun we had unlocking the dormant cores in the Cayman GPU with the HD 6950.

Sadly while we were able to boot with the HD 7970 BIOS on the HD 7950 it didn't unlock the extra 256 Radeon Cores. And it didn't help with stability either…

Verdict

The AMD Radeon HD 7950 is one hell of an impressive pixel-pusher, and Nvidia is going to have to work incredibly hard with its Kepler cards to best this excellent card.

]]>

Artikel Terkait: