AMD Radeon HD 7870 £260
5th Mar 2012 | 09:42
An unassuming graphics card... 'til you unleash the beast within
At long last the line up is complete, with the AMD Radeon HD 7870 and AMD Radeon HD 7850 finishing things off for AMD's next generation graphics family.
Yes, we've seen the (almost) very top-end of AMD's graphics stack, with the AMD Radeon HD 7970 and Radeon HD 7950, and recently we've seen the bottom end of its Graphics Core Next (GCN), 28nm Southern Islands set with the AMD Radeon HD 7770 and Radeon HD 7750.
Why do we say almost the very top-end?
Well, so long as AMD stays true to form we should expect to see a dual-GPU card based on the Tahiti GPU of the HD 7900 series cards before too long. That AMD Radeon HD 7990 (it's not much of a stretch to think it'll follow the naming conventions of the AMD Radeon HD 6990) will represent the pinnacle of AMD graphics.
And is likely to be sitting somewhere in the region of £600-£700. Eek.
But that ridiculous end of the graphics market is not what we're looking at with the AMD Radeon HD 7800. This here represents the start of its enthusiast range of cards; serious gaming starts here, according to AMD.
These are, according to AMD, the cards for gamers wanting to hit the highest graphics settings in-game without having to spend £300 on a GPU.
That's a very laudable position, but not something that's necessarily that new.
At the top end of the graphics market the air is rarefied and there's not the wealth of competition there is around the same sort of price-points that exist lower down the GPU ladder.
At the point where AMD is aiming the Radeon HD 7870 and Radeon HD 7850 there is already a host of enthusiast-class graphics cards they're going to have to do battle with. And typically not all of them are made by the competition.
The Radeon HD 7800 series, code-named Pitcairn after the wee south pacific island with a population of three rather mangy cows, a dachshund named Colin, and a small hen in its late forties, is meant to sit in the gap made by the Tahiti-class and Cape Verde-class cards.
That's a price range to hit between £120 and £350; a rather wide, and GPU-packed expanse to fill with two cards.
So there's a lot of competition out there for the AMD Radeon HD 7870 to cope with, what tricks does it have up its sleeve to combat the best of the rest?
Unlike the previous Northern Island generation of cards the top two series of the Southern Islands generation of GPUs have a lot in common with each other.
Both the Radeon HD 7900 and Radeon HD 7800 series GPU are based on the same GPU architecture with just a few of the Compute Unit building blocks removed from the lower caste GPUs.
Contrast that with the HD 6900 and HD 6800 series cards, where they used different instruction sets, and you can see you're not losing out architecturally with the AMD Radeon HD 7870.
The Cayman GPU of the HD 6900 cards was built using AMD's then brand new setup, the VLIW5 architecture, while the HD 6800 series (and below) were based on the previous generation's HD 5800 series VLIW5 architecture.
We can forget all about the Very Long Instruction Word (VLIW) GPUs now though as AMD has completely ditched that design in favour of a scalar processor design more in line with what Nvidia has been doing for the last few years.
Without re-treading too much of the ground we trod with the AMD Radeon HD 7970 architectural review, the original AMD tech sorted out instructions into batches before pushing them off down the GPU pipelines.
For fixed-function graphics work, like gaming, it was a great solution.
The Graphics Core Next GPU though is built of Compute Units (like Nvidia's Streaming Microprocessors) which are like tiny, self-contained processors.
The resulting chip then has lots of these little processors which will each work on one instruction at a time until all the work is completed.
This means that for varied GPGPU tasks the more flexible architecture should produce better results.
To make sure it's still gaming-capable though there are four vector units in each CU to make for a combination of its old-school vector processing and the scalar architecture.
The HD 7870 has 20 of these Compute Units, making a total of 1,280 stream processors. Compared with the 32 CUs and 2,048 shaders of the HD 7970 and the 28 CUs and 1,792 shaders of the HD 7950 that's quite a drop.
It also means that the AMD Radeon HD 7870 also looks a little shader-poor when compared with even the relatively lowly HD 6950. That card's got a decent complement of 1,408 stream processors in its make up.
With the 28nm process and very different architecture though that makes it a bit of an apples vs. llamas comparison.
Like the AMD Radeon HD 7900 series cards, the HD 7870 also comes with twin geometry engines, making for some serious tessellation performance; which makes absolute mincemeat of the HD 6900 series in theoretical tessellation benchmarks.
That said in basic teraflops terms the AMD Radeon HD 7870 is still a little behind its HD 6970 grandad. The 1,536 shaders of the elderly VLIW4 architecture pumps out around 2.7 TFLOPS of raw GPU processing power while the HD 7870 is batting around the 2.5 TFLOPS mark.
Performance at the AMD Radeon HD 7870's stock speeds isn't particularly spectacular. Compared with the HD 6970 there isn't a lot of extra performance in the newer silicon. In certain cases the older card actually takes a bit of a lead.
That said in the very niche field of tessellation, in both OpenGL and DirectX 11 APIs, the HD 7870 takes the previous generation to task.
Thanks to the massive amount of performance headroom AMD has deliberately left these chips with you can push them well over the already high reference clock to something that will make the more expensive Nvidia cards sit up and take notice.
When you can rival the competition's top single-GPU card with your mid-range card then you know you're doing something right.
DirectX 11 tessellation performance
OpenGL tessellation performance
DirectX 11 gaming performance
To be perfectly honest, although we didn't like the use of last-gen technology in the HD 6870 vs. HD 6970 in the previous generation AMD could have easily gotten away with doing the same thing in the Southern Island generation.
The scalar AMD Radeon HD 7870 doesn't really have a lot extra straight-line performance in the tank over the VLIW-sporting HD 6970.
AMD could easily have modified the Cayman GPU to make for a well-performing new card in this space, or even just rebadged the older GPUs. It would've gotten away with it too, with but a little media grumbling.
Thankfully though AMD has stuck to its guns and produced a proper GCN-powered mid-range card to sit in the same price and performance space as its last-gen top-end card, the HD 6970.
It's not looking at the release of the HD 7870 as the card for owners of either of the Cayman-powered cards to upgrade to. Instead it's been talking about the Pitcairn cards as the "spiritual successor to the HD 5800 series graphics cards," as Evan Groenke, Product Manager at AMD said in a recent briefing.
AMD sees the two year upgrade cycle leading owners of HD 5800 series cards, now looking to upgrade, towards the HD 7800 series as the entry point to enthusiast-class gaming.
The reason for this is that there is simply no performance incentive for anyone with a HD 6900 series to make the move.
We'd normally expect mid-range cards of a new generation to perform at the same speeds as the previous high-end cards and that certainly is true here. The only issue is that they are also the same price as the previous high-end cards.
The difficulty then is that we've had graphics cards capable of performing at the levels the AMD Radeon HD 7870 operates at, in the same price-bracket, for the last year. Sadly then that makes the release of the HD 7870 rather a flat one.
But as we say kudos to AMD for not just going down the easy route.
We may not be getting any major price/performance scores from the AMD Radeon HD 7870, but it still comes with all the goodness of the GCN-based Southern Island cards.
That means an efficient 28nm production process, PCI Express 3.0 support and the excellent AMD ZeroCore Power technology.
The benefits of the production process means that as we go forward the cost of manufacturing these chips should drop allowing AMD to pass some savings on to us. It also means that as we are the start of this new GCN technology we should also see some driver-based performance improvements over the next year, like we've seen with other AMD GPUs.
The inclusion of the ZeroCore Power tech is also important, giving us impressive power savings when the PC is in an idle state. AMD's latest cards can almost entirely shut down when the monitor is not displaying, using only ten per cent of the idling power of their predecessors.
What we haven't spoken about yet though is overclocking, and like the HD 7970 and HD 7950 it's something the AMD Radeon HD 7870 does with aplomb.
And the overclocking is also something of a game changer.
We were able to knock the GPU clock up from the already impressive 1GHz mark up to 1.2GHz using just a little higher fan speed and the built in Overdrive tool of the Catalyst Control Centre.
Granted the stock fan is loud even at 50%, but it enabled us to run rock solid at those heady OC heights. And running at those speeds suddenly the Nvidia GeForce GTX 580 is right in its sights; that's a card which still costs £360.
We can't assume that every AMD HD 7870 is going to be able to clock up to those speeds, but with even the reference design starting out at 1GHz we wouldn't be surprised to see most being able to get pretty close.
Being able to perform at the same levels – sometimes even faster – than a card worth £100 more is something not to snotted at.
Even so we would struggle to recommend it as an upgrade to anyone already sitting on either a HD 6970 or GTX 580, but as AMD says, for an enthusiast who hasn't upgraded in a couple of years this is the go-to sub-£300 card.
The fact AMD has included the full Graphics Core Next feature set is something to be applauded.
It may not have the straight performance edge over the previous generation, but it's got a lot more extras to back it up.
We can't ignore the awesome overclocking potential in the Pitcairn chip either. There's no guarantee all AMD Radeon HD 7870s will be able to clock this high, but there is at least precedence.
The HD 7870 is not a massively exciting card if you're not prepared to thrash it with the overclocking stick.
Stock performance is on the same level as the previous gen cards, and for the same price. In those terms it really does nothing new.
At stock speeds it's fairly dull, with a little light tweaking however you can turn it into a serious hot hatchback with the horsepower to match.