There’s never been a better time to upgrade your CPU or to put together a new custom-built system. Intel’s Sandy Bridge processors offer unprecedented performance for their price, while older Westmere parts are becoming ever more affordable. In the opposite corner, AMD is offering a huge range of processors at cut-throat prices, ensuring there’s something for everyone.
But with so much choice on offer, it’s difficult to know which way to leap. Is it worth paying for a model with a high clock speed, or is the benefit marginal? How many cores do you need, and is Hyper-Threading worth it?
The only way to know is to put the silicon to the test. That’s why we subject the complete range of mainstream AMD and Intel processors to our brand-new Real World Benchmarks this month (detailed on p38). Our tests expose exactly how each one performs in Windows, in typical media-processing duties and in heavy multithreaded use, to help you identify the perfect processor, no matter what your workload.
With the results in, we weigh the performance against the street price of each contender to identify which processors break the records but not the bank, and which ones are a total waste of money. If you’re thinking of buying a new PC, or treating yourself to a processor upgrade, you’d be mad not to read this first.
There’s a bewildering range of CPUs on the market, starting at less than $40 and going up to over a thousand dollars. Broadly speaking, you get what you pay for, but there are many factors that determine how a CPU will perform in a given role – a CPU that’s perfect for one task might be underpowered for another. Equally, if you don’t choose carefully, you could end up paying for expensive features that you don’t need.
A processor’s performance is partly determined by its clock speed, expressed as a frequency in gigahertz. This isn’t the only thing that determines performance – that old misconception used to be known as the megahertz myth. But if you’re comparing two processors from the same range, such as the AMD Phenom II X4 910 and X4 945, a higher clock speed should translate to faster performance. The difference may be less than expected, though, due to bottlenecks elsewhere. On paper, the X4 945 is 15% faster than the X4 910 but, in our real-world tests, we found the effective gap was less than 10%. Clearly, clock speed is only a rough guide to performance.
It’s worth noting that some of these processors come with unlocked clocks, enabling you to increase their speed above the stock frequency. Even processors that aren’t unlocked can often be tweaked for a free speed boost. See Overclocking: what’s the frequency? on p65 for more information on the dark arts of overclocking.
Almost all modern CPUs have multiple cores, making your system more responsive when running several tasks at once. Some programs (such as 3D rendering applications) can divide their workload into multiple threads, and send different threads to different cores to be processed simultaneously, yielding big performance gains.
Thus, while a dual-core CPU is fine for everyday web browsing, you’ll find a four- or six-core processor makes things faster and more responsive if you do video processing or heavy multitasking. Most Intel processors offer a feature called Hyper-Threading, which allows one core to service two threads at once. A quad-core Core i7 will thus appear to Windows as an eight-core processor – but performance in heavily multithreaded tasks is nowhere near as good as you’d see from a real eight-core CPU.
Most Intel chips also use a feature called Turbo Boost, which automatically diverts power from unused cores to raise the speed of the ones that are being used. AMD uses a similar system called Turbo Core on its Phenom II X6 processors. Multicore technology can thus assist single-threaded workloads as well as multithreaded ones.
Bus speed and cache memory
The CPU is the fastest component in your PC, so it inevitably spends some of its time waiting for information from the memory and other parts of the system. The speed of the bus that carries that information can thus have an impact on performance. AMD processors use a bus called HyperTransport, which normally runs at 2GHz. Intel’s bus technologies run at various speeds.
While a faster bus can assist overall performance, it’s better for the CPU to keep information in an internal memory cache, from which it can be accessed almost instantly. This cache comes in three levels: L1, the smallest and fastest cache; L2, which is a larger secondary storage area for individual cores; and L3, which is shared between all cores.
Cache memory can have a significant effect on overall performance – compare AMD’s Phenom II series, with its 6MB L3 cache, to the Athlon II chips, which lack L3 cache.
This month, we’ve tested every mainstream CPU on the market, using our new Real World Benchmarks to measure overall responsiveness as well as performance in media and multithreaded tasks.
You’ll find a breakdown of overall performance against price on the next page. A list of core features and a breakdown of performance results can be found on the review pages to the left. We also look at each family of processors in depth, examine the strengths and weakness of each model, and award scores out of six for value and performance, to help you identify the stars of the show.
The graph on this page plots the online price of each model against its overall score in our benchmarks. As in previous CPU megatests, it’s the models nearest to the bottom-right corner that give the best bang per buck. If a chip is unlocked (see feature table, opposite), you can increase its settings to gain a performance boost beyond the scores shown here.
Most Intel processors now come with a built-in Intel HD Graphics module. These GPUs aren’t powerful enough to run complex 3D games, but they’re an inexpensive and power-efficient way to run Windows, watch high-definition movies and play lightweight games.
If you want to use the HD Graphics on an Intel chip, make sure you partner it with a motherboard that supports it, since not all boards do. Current AMD processors don’t come with built-in graphics, but you can buy an AMD motherboard with an integrated GPU to achieve the same effect.
Right now, the best balance of performance and value comes from Intel’s Sandy Bridge (socket 1155) chips. Their benchmark scores snake out far beyond anything AMD has to offer – and indeed beyond the best of Intel’s own socket 1156 range – yet even the top-end models are comparatively affordable.
If you’re looking for a mid-priced desktop processor that will breeze through today’s most demanding applications, look no further.
For those who demand maximum parallel processing power, the older Core i7s in the 1366 package may still have a role to play. They’re the only chips that can beat Sandy Bridge, with multitasking performance a particular strong point. But, as the graph makes clear, pricing is erratic, with the similarly-performing Core i7-970 costing twice as much as the Core i7-2500.
If you’re on a more modest budget, AMD comes into its own. The Phenom II X4 series gives strong performance at reasonable prices, and if you pick a Black Edition, you can tweak the clock speed to rival, or even beat, the latest Core i3s.
Squeeze the price more tightly and the best value comes from the Athlon II X2 series for basic computing power. The Sempron processors are the cheapest here, but their performance is so poor it’s off the left-hand side of our graph; we can’t recommend them for any desktop role.
Clearly, Sandy Bridge is setting the pace of the market as a whole. In terms of future support, it’s the safest platform to invest in. Intel’s 1156 range will surely be phased out before long, since it’s no longer economical, and a successor to the 1366 platform is expected before the end of the year. AMD’s AM3 socket is also due for an upgrade this summer, to accommodate the firm’s forthcoming Fusion processors; it could be worth waiting to see what happens next.
Yet, this is always the way with technology: there’s always something newer around the corner. So if any of this month’s CPUs fits your needs, we suggest you dive in, enjoy your purchase and don’t look back.
To fairly compare the dozens of CPUs on the market, we subject them all to our new benchmark suite, in configurations as similar as their differing architectures would allow.
Each chip is tested at its stock speeds, in a mainstream motherboard with 4GB of 1066MHz of DDR3 RAM and a 1TB, 7200rpm hard disk. Although some processors have built-in graphics, we use a low-end AMD graphics card in all our tests, to ensure a level playing field.
Overclocking: what's the frequency?
Overclocking means running your processor above its normal speed. It’s a potential way to get a free performance boost, but it isn’t always plain sailing. Push the speeds too high and you’ll make your system unstable; in the worst-case scenario you could even damage your CPU.
However, both AMD and Intel have effectively given overclockers their blessing by offering unlocked models of their processors that can be freely ramped up to any speed you like. If you’re in the market for a new CPU, it’s an option well worth considering.
How to do it
Your CPU speed is driven by the “base clock” of your motherboard. On AMD systems, this generally ticks along at 200MHz; for Intel boards, it’s 133MHz. Clearly, this is far too slow for a processor, so a frequency multiplier is applied to get the CPU up to speed. For example, a 3GHz AMD processor uses a multiplier of 15 to achieve its advertised frequency.
Ordinarily, your motherboard will automatically apply the default multiplier for whichever processor is installed, but if you go into your BIOS settings you can easily change this value. On locked chips, the multiplier won’t go above its default value, but with an unlocked chip you can raise the multiplier as high as you like. On Intel chips with Turbo Boost, you can also adjust the Turbo multipliers, to set even higher speeds when all the cores aren’t in use.
These tweaks are simple to apply, but different motherboards present them in different ways: if you can’t find an option to adjust your CPU multiplier, check your documentation or search the web for help.
Risks and challenges
It’s sometimes suggested that overclocking harms CPUs. That’s a valid concern, especially because damage caused by manually overdriving a processor won’t be covered by any warranty. But as long as you proceed sensibly, and don’t push your CPU frequency so high that it overheats on a regular basis, you shouldn’t have a problem.
Unfortunately, there’s no easy way to find that frequency. All you can do is experiment in your BIOS and try to find the highest settings that will keep the system stable, even when the CPU is under heavy load for a prolonged period. It’s worth downloading a tool such as the free CoreTemp utility (www.alcpu.com/ CoreTemp/) to give advanced warning of potential overheating.
You could also invest in an upgraded heatsink and fan that draw more of the heat away and keep things stable at higher frequencies. Die-hard enthusiasts invest in huge propeller-type arrangements and water-cooling tanks, but companies such as CoolerMaster and Thermaltake offer more modest options starting at about $30.
View from the Labs
The phrase Sandy Bridge echoes through almost every page of this month’s CPU megatest. We’re sorry if the repetition is a little tiresome, but it’s inevitable, because the simple fact is that Intel’s Sandy Bridge chips set the new standard against which every other processor must be judged.
It isn’t only Sandy Bridge’s performance that makes it special – although that’s formidable, to be sure. Rarely has a new generation of processors ever delivered such a leap above the previous generation. Consider that the 32nm Westmere processors were launched little more than a year ago, and it isn’t only a large step forward, it’s an impressively rapid one.
What’s really revolutionary about Sandy Bridge, however, is its pricing. Hitherto, Intel has tended to position its processors on a steep curve, with prices that rise sharply as you move up from low-end. Look at the older Core i5s, or the top-end Core i7s that make up the 1366 platform, and you can still see that curve broadly in effect.
Now – as a glance at our graph on the other page reveals – Intel has changed the game. No longer does the top-end part cost four times as much as the entry-level model. Today, even the aspirational Core i7 models are perfectly affordable for a mainstream desktop. To a greater extent than ever before, you really do get what you pay for.
This abrupt change of tack is a gutsy move by Intel. Even if the company is planning to retire the older Socket 1156 platform – something it hasn’t formally confirmed – there’s still a big stockpile of last-generation Core i3 and i5 chips out there, particularly in laptops, which are now significantly devalued. It’s the same story with the Socket 1366 platform. Sandy Bridge’s aggressive new pricing scheme yanks the rug from under all of its predecessors.
Is that a bad thing? For anyone looking to buy a new PC, it’s great news. And it could prove to be a shrewd move for Intel too. After all, while the chip giant is undercutting itself, it’s also undercutting its rival AMD. In the past, we’ve regularly praised Phenom II X4 and X6 processors for offering an affordable alternative to Intel, but most of those models now look underpowered and overpriced. It raises the bar for future launches, too: when AMD’s new Fusion desktop processors arrive, they might have to sell at much thinner margins than the manufacturer had hoped.
In all, Sandy Bridge is a stiff challenge to AMD, both technologically and financially. Unless AMD has something special up its sleeve, Intel’s irresistible combination of power and price could see it dominate the CPU market for the next five years, just as it has the past five. If that means more releases in the vein of Sandy Bridge, we say bring it on.