AMD's APU technology - combining CPU and GPU in one chip - is well-known for offering up entry-level gaming power that significantly outperforms the Intel equivalents, usually at a very competitive price point. But in the last few months, the technology has upped its game. With the arrival of Xbox One and PlayStation 4, we've seen APU tech move on to the next level, defining the next generation of console gaming, while the latest PC desktop equivalent - codenamed Kaveri - promises to completely revolutionise the relationship between CPU and graphics tech in a way that simply isn't possible in a conventional computer.
This key new technology is called HSA - Heterogenous System Architecture - and it utilises the currently unique ability of the main processor and its GPU compute units to simultaneously access the same memory space, allowing for both components to work on the same tasks in tandem without having to shuttle data back and forth across constricted interfaces. It's an exciting technology, allowing apps to more easily take advantage of the very different processing strengths and weaknesses of the CPU and GPU architectures, with neither relegated to second-class citizen status.
The really impressive thing about HSA is that all of this cooperation between the two processing units is entirely invisible to the software - the API itself takes care of all the heavy lifting. Results in demos so far look promising, but really we're looking towards the longer term before we start seeing HSA make a genuine difference to everyday computing. Perhaps the biggest disappointment in reviewing Kaveri is that one of its most exciting new aspects currently has little relevance either to general computing or gaming.
However, Kaveri still has much to offer - specifically gamer-friendly enhancements such as integration of the firm's most recent GCN (Graphics Core Next) architecture, meaning support for the new Mantle API. Alongside that, there's dedicated TrueAudio processing silicon, which AMD reckons can significantly reduce the CPU burden on computationally expensive effects such as reverb. There are also refinements to the CPU architecture itself, which sees Steamroller take over from last year's Piledriver - bringing about improved performance plus better power efficiency. The A8-7600 we're testing has the ability to run at a miserly 45W and still hand in decent entry-level gaming performance, with the BIOS offering up the chance to "upgrade" to 65W, boosting CPU frequency - though GPU remains unchanged. Either way, we benched our entire system at just 90W during the taxing Metro: Last Light benchmark, which is pretty impressive stuff (and that's with the processing running at the 65W level).
But to what extent can this system cope with gaming? Can it keep up with the latest and greatest titles? AMD has targeted 1080p gameplay at 30fps, but previous APUs have been much more comfortable in the 720p/768p arena. For all its improvements over last year's Trinity and Richland chips, by our reckoning it would take a massive leap in power to provide that kind of performance in a sustained manner. The A8-7600 is curious in that you can switch between 45W/65W TDPs, so we engage the higher power limit in order to give our games as much CPU processing power as possible. Overall, Kaveri hands in a pretty impressive showing, but as our Battlefield 4 testing at the medium quality level demonstrates, we're still some way off achieving anything like a consistent experience at full HD resolution. On the more taxing games at least 720p/768p remains the target, but there's enough horsepower on tap to push the quality settings significantly beyond what can be achieved with the same games running on Xbox 360 and PlayStation 3.
It's fair to say that BF4 is a fairly challenging game from a tech perspective - especially on the South China Seas aircraft carrier setpiece - so we rolled out our existing range of benchmark titles to see how they fared with the new APU. However, judging exactly what to bench was quite challenging. After all, the 384 GCN stream processors in the A8-7600 are exactly half that of the Xbox One, while frequency is limited to 720MHz, up against the 853MHz in the new Microsoft console. We're looking at some kind of midway point between last-gen and next-gen console performance.
However, the real challenge Kaveri faces is the fact that the GPU component has no access to ultra-fast GDDR5 RAM - instead, the DDR3 RAM installed on the motherboard is utilised for graphics tasks - something for which it wasn't really designed as the raw bandwidth simply isn't there. There's been a lot of talk about AMD potentially releasing a powerhouse APU for PC based on the PS4/Xbox One designs, but in the absence of GDDR5 or a similarly fast equivalent, that really doesn't make sense - the compute units simply couldn't be fed data fast enough. That said, DDR3 comes in many flavours: the faster the RAM you have, the better Kaveri performs. For the complete system that AMD supplied, the firm took no chances, fitting enthusiast-standard 2133MHz modules in a dual-channel configuration.
In addition to running our standard benchmark suite, we also spent some time playing the games, with Tomb Raider in particular occupying much of our time. On medium settings, the game was essentially unplayable at 1080p, while 1600x900 gave console-style performance - albeit with some real fluctuations in frame-rate whenever the game utilised water effects (or any other kind of alpha) extensively. In short, even with 2133MHz RAM, you're constantly battling RAM limitations.
To give a decent idea of how well the A8-7600 works across a range of gaming conditions, we ran the same titles on the same medium settings across three resolutions: 1280x720, 1600x900 and 1920x1080. It's telling that only Sleeping Dogs showed any sign of being playable at 1080p, suggesting that lower resolutions are essential for a fluid experience on any modern game. We feel we could work with 1600x900, but perhaps unsurprisingly the APU provided the best performance on all titles tested at 720p - indeed, outside of the benchmark during actual gameplay, we could even run Tomb Raider at high settings with consistently decent frame-rates. It felt almost like a high-end PC experience, just running at Xbox 360 resolution.
"Limited GPU resources and comparatively slow RAM access limit Kaveri's potential, but wise settings selection and realistic resolution choices yields good results."
|BioShock Infinite, Medium||47.3fps||33.7fps||25.2fps|
|Tomb Raider, Normal||55.1fps||38.1fps||27.8fps|
|Metro 2033, Medium||42.2fps||32.5fps||26.0fps|
|Metro: Last Light, Medium||34.3fps||25.8fps||19.6fps|
|Hitman: Absolution, Medium||36.1fps||28.8fps||23.1fps|
|Sleeping Dogs, Medium||59.6fps||45.2fps||27.2fps|
So in theory, Kaveri's looking pretty decent at this point, but one thing bothered us during our testing: AMD's APUs are geared towards entry-level gaming PCs and yet the test unit is packing high-end memory that out-specs the more mainstream 1600MHz modules routinely found on the market today. Indeed, RAM prices have shot up over the last year, and often the best deals to be found involve locating older 1333MHz stock. Our worry was that this review would not be indicative of real-life performance because an entry-level processor was seeing its results augmented via enthusiast-standard RAM.
Dipping into the BIOS, we reduced frequency down to 1333MHz, 1600MHz and 1866MHz in an effort to emulate the performance of RAM modules more likely to be paired up with the new APU. Then we re-ran the 720p benchmarks to see what impact the reduced bandwidth had on gaming frame-rates.
The results are enlightening. Stepping down from 2133MHz to 1866MHz offers the smallest drop in performance - around seven per cent all told - but that figure moves into the double digits as you drop down from 1866MHz to 1600MHz, and then again from there down to 1333MHz. Comparing the slowest memory tests to the fastest, we find that 1333MHz DDR3 dual-channel frequencies offer around 78 per cent of the performance of the fully maxed out system, and a fundamentally different gameplay experience.
Also, suffice to say that you'll need to use two matching memory modules in order to utilise dual-channel operation, otherwise you're looking at an enormous drop in throughput, effectively crippling the APU. Utilising two sticks of RAM is pretty much the norm on most PCs, but during recent testing on another project we're working on, we found that using just one stick of RAM had negligible impact on gaming frame-rates on a traditional gaming rig with a dedicated graphics card. Onboard GDDR5 seems to be a far, far more important component to gaming performance on a standard gaming PC as opposed to single or dual-channel RAM, or its speed.
"Available memory bandwidth is hugely important for Kaveri, which could be a problem for a budget processor likely to be matched up with slower mainstream DDR3 modules."
|BioShock Infinite, Medium||47.3fps||44.4fps||40.1fps||36.4fps|
|Tomb Raider, Normal||55.1fps||51.5fps||48.2fps||43.7fps|
|Metro 2033, Medium||42.2fps||39.4fps||35.2fps||31.2fps|
|Metro: Last Light, Medium||34.4fps||32.0fps||28.3fps||26.1fps|
|Hitman: Absolution, Medium||36.1fps||33.3fps||30.2fps||27.2fps|
|Sleeping Dogs, Medium||59.6fps||55.3fps||51.2fps||46.9fps|
Overall results during our testing weren't bad at all, bearing in mind the cost of the A8-7600 and the really tight TDP window the processor has to operate in. We gave Mantle a quick test and can confirm that it is fully armed and operational on the latest 14.1 AMD beta drivers, and it provides a small uptick in performance on Battlefield 4 - just as long as you don't engage v-sync. The game seems to disagree with it massively, crippling performance levels in comparison to the standard DirectX 11 renderer.
AMD Kaveri A8-7600 APU - the Digital Foundry verdict
With the arrival of Kaveri, we're looking at a revolution in the relationship between the CPU and GPU, with HSA bringing us one step closer to the day where apps automatically allocate tasks according to the processing resources best suited to carrying them out. AMD had to start somewhere in providing a platform for developers to work with, but in the here and now there's little software available that allows us to test the technology in a way that's meaningful to gaming or everyday computing. Obviously we should expect to see that situation change in the fullness of time, but in the meanwhile, we can only really assess Kaveri in terms of its performance on standard tasks and gaming, and there we find some interesting results.
First of all, AMD has worked some magic in terms of making its Steamroller cores much more effective at the 45W and 65W levels, handing in good performance in relation to its more power-hungry predecessors. There's nothing here to stop the Intel juggernaut in terms of all-out performance, but there's a good balance regardless. Secondly, the transition to GCN graphics hardware is clearly a step in the right direction, again offering excellent efficiency compared to last year's APUs. However, we're very much looking at entry-level gaming here - 720p and 900p offer the sweet spots in terms of image quality and frame-rate. The 1080p dream really is off the table for modern titles - though perhaps the additional compute units found in the much more expensive A10-7850K would make the difference.
"The Mantle API shows a genuinely worthwhile boost to Battlefield 4 performance if Kaveri is coupled with a meaty GPU. On limited APU graphics we only noted a modest improvement."
On the one hand, a Kaveri PC potentially offers exceptional value. Assuming the $119 US price point of the A8-7600 we tested translates into a sub-£100 sticker price in the UK, you're effectively getting ballpark Core i3 performance with decent entry-level graphics thrown into the bargain. However, with APU technology as it stands right now, serious gamers are likely to run up against limitations in either CPU or GPU performance and the upgrade paths are unclear. CPU-wise, you're effectively stuck until the next APU comes out, with no hex or octo-core AMD upgrades options available for this platform.
If - as is likely - you'll hit GPU limits, the obvious choice is to buy a discrete graphics card, but move too high up the stack and the existing, effectively non-upgradable CPU will bottleneck performance, in which case AMD's own AM3+ platform, or Intel's socket 1150 simply opens up so many more gaming options. We were unable to test hybrid Crossfire - which sees users adding a discrete GPU to the existing APU graphics - but historically that hasn't offered great value on APU systems. To see a real boost to graphics power, effectively you need to replace the APU's own GPU, making it a waste of silicon. In short, Kaveri is the undisputed king of its own niche, but this is not the best platform to buy into if your gaming aspirations are likely to exceed the limits we've set out in the benchmarks above.
In many ways, Kaveri is the start of something genuinely new and exciting. Many of the innovations found in the next-gen consoles are here - the ability for GPU and CPU to address the same memory space for example, along with dedicated audio handling, plus there's all the promise of HSA, wherever that may take us. The foundations are here for something exceptional, but we're a generation or two away from the tech really finding its feet. In the meanwhile, what we have is a lovely entry-level gaming platform, but with just a few too many limitations for our liking.
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