Chip Showdown: A guide to the best CPUs on the market

Confused about which processor to pick for your new system? We tested leading chips to help you make the smartest choice

5. AMD Phenom II X4 945

Chip Showdown

Benchmark Score: 110

If multithreaded applications aren't your deal, AMD's Phenom II X4 945 is a powerful alternative to its top-shelf Phenom II X6 1090T processor.

AMD released its first Phenom II processors, the quad-core "Deneb" CPUs, in January 2009. Triple-core X3 processors (whose performance falls between that of their dual-core and quad-core cousins) followed. Arriving a few months later was the 3.0GHz X4 945 processor, which brought full AM3-socket support. The benefit of this design is that AM3 will allow you to stick DDR3 memory in your system.

This $181 quad-core chip runs a mere 7 percent slower on our WorldBench 6 tests than AMD's top-shelf, six-core Phenom II X6 1090T. The chips have similarities--the X6 is akin to an X4-class processor with two extra cores bolted on. Both share 6MB of L3 cache and run on a 2GHz HyperTransport architecture (the AMD analog to Intel's QPI), but the X6 1090T runs at 3.2GHz, with automatic overclocking up to 3.6GHz. On Cinebench, the six-core X6 1090T outperforms the quad-core X4 945 by 60 percent.

6. AMD Athlon II X4 635

Chip Showdown

Benchmark Score: 110

The Athlon II X4 635 shows that omitting a processor's L3 cache isn't necessarily a crippling blow to performance.

Does your system really need a ton of L3 cache in order to achieve dazzling performance? For all intents and purposes, AMD's 2.9GHz Athlon II X4 635 processor is the functional equivalent of its 3.0GHz Phenom II X4 945. Both CPUs are based on the AM3 socket, though the X4 945 sports a 15X multiplier instead of the Athlon II X4 635's 14.5X, for a slight difference in clock speeds.

The $129 X4 635 runs on a smaller die size, compared with the Phenom II X4 945. The biggest difference between the two chips is the omission of the Phenom II family's L3 cache. This doesn't affect the overall WorldBench 6 score of the Athlon II X4 635, however, as it's able to tie the Phenom II X4 945's score of 110. That said, Cinebench results show that the latter CPU is a stronger multitasker, but only to the tune of a 9.5 percent increase in performance.

7. Intel Core i5-750

Chip Showdown

Benchmark Score: 106

You don't get multithreaded processing power with the i5-750; as a result, this quad-core suffers on multitasking tests.

This 2.66GHz quad-core CPU, a member of Intel's Lynnfield family of chips, is based on the same characteristics as the previously mentioned Core i7-870 CPU, with one key difference: This CPU has no hyperthreading--its four physical cores are all you're going to get, rather than the eight "virtual cores" that would otherwise appear in your operating system when using a Core i7-870.

How much does that difference affect this $276 chip's performance? Our WorldBench 6 tests showed a 17 percent drop by the i5-750 from the i7-870, which is almost double the 9 percent difference be­­tween the two CPUs' stock clock speeds (the i5-750, with Turbo Boost, can raise its frequency to 3.2GHz when needed). The difference on our multithreaded Cinebench test is more pronounced, as the i5-750 delivers a score 40 percent lower than that of the i7-870.

In addition to the chip's dual-channel memory controller (which means only four DIMM slots), the socket-1156 CPU's internal PCI Express controller can dish out one full x16 PCI-E connection for graphics or split two x8 connections. That won't affect your performance unless you plan to run a pair of graphics cards in parallel.

8. AMD Athlon II X2 255

Chip Showdown

Benchmark Score: 101

This low-end CPU isn't that much slower than the Phenom II X6 1090T, except with multithreaded apps, where it's game over.

AMD's US$82, 3.1GHz dual-core Athlon II X2 255 doesn't come with any onboard L3 cache. And its L2 cache (memory that's typically smaller, faster, and located closer to the core) is split into 1MB per core. As a 45-nanometer, Socket AM3 model, it's backward-compatible with any motherboard based on Socket AM3 or AM2+.

As for performance, when compared with AMD's top-shelf, six-core Phenom II X6 1090T, the X2 255 is only 15 percent slower on our general tests--but 70 percent slower on Cinebench, our multicore-focused measure. For another comparison, although the X2 255 runs at a higher clock speed than the quad-core, 2.9GHz X4635, the latter's two extra cores help it deliver an 8.9 percent increase in performance on our WorldBench 6 tests, and a whopping 83.6 percent increase on our Cinebench test.

Next page: CPU Terms, New Chip Tech on the Horizon, Server Chips

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