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CPU Megatest: 59 chips reviewed and rated
Staff Writers | Apr 1, 2011
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CPU Megatest: 59 chips reviewed and rated
We put every mainstream desktop processor from AMD and Intel through our brand-new 2011 real world benchmark.

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.
 

Clock speed



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.
 

Multicore processing



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.
 

Our ratings


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.
 

Integrated graphics




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.

Products in this Group Test

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