Labs

The Athlon 64 X2 was AMD's first dual-core processor for the desktop PC, and it's still going strong thanks to its move from Socket 939 to AM2 earlier this year. With this move came the addition of virtualisation technology to the range, as well as support for DDR2 memory, bringing it in line with Intel's top-of-the-range CPU families.

All models support virtualisation, NX-bit security and, naturally, they're still 64-bit CPUs. They all operate with a HyperTransport frequency of 1GHz and support Cool'n'Quiet for maximum energy efficiency during idle moments. The move to AM2 brought a reduction in TDP to 89W, but AMD has also released Energy Efficient Athlon 64 X2s, which cost a little more but result in a lower TDP of 65W. They tend to cost more for the privilege.

Until very recently, the Athlon 64 X2 family comprised the 2GHz 3800+ up to the 2.6GHz 5000+. Initially, much like the Semprons, there were two CPU models at each clock speed, one with a pair of 512KB Level 2 caches and the other with twice that amount. But in June 2006, preferring to consolidate the line, AMD put an end to the 2 x 1MB models, which means there are very few available to buy.

We've included them here (the 4000+, 4400+ and 4800+), but their high prices make them poor value. To confuse things further, AMD recently announced a new 2 x 1MB model, the 2.6GHz 5200+, so the family now consists of just five processors - the 3800+, 4200+,

Value for money

Since the move to the AM2 platform excludes the old Athlon 64 processors from this test, there's a gap in prices between the top-end Sempron and the X2 3800+. If you have an AM2 motherboard and a limited budget, you'll need to decide whether to go for the single-core Sempron 3600+, which scores 0.79 and costs £57, or the dual-core 3800+, which costs nearly £30 more yet scores 1.05. If you can stretch your budget to £85 for the X2 3800+, we'd recommend the flexibility of a dual-core system for all but the most undemanding users.

The X2 3800+ is the best-value processor at the lower mid-range, as it costs the same as the Pentium D 925 (which scored 0.94) and the much slower Pentium 4 630. To emphasise the 3800+'s good value, the comparable Intel performer is the Pentium D 945, yet it costs £97 and is one of the cheaper among its family.

With each step upward, the increase in performance is more or less constant, but the price premium is greater. For example, the jump from the 3800+ to the 4200+ is £18; from 4200+ to 4600+ it's £31; and from 4600+ to 5000+ it's £45. So the value drops the higher up the range you look. The 5200+ is a slightly different prospect, as it's only 4% faster than a 5000+, yet the 1MB of cache for each core gives a significant boost in certain applications, such as - in our tests - Microsoft Office. Whether it's worth the extra cost will depend on how much (and how intensely) you use Office.

Overall, the Athlon 64 X2 3800+ is the pick of the bunch, but bear in mind that past the 3800+ prices move very much into Core 2 Duo territory, and the Athlon 64 X2 struggles more and more to match its rival for value as the speeds increase.

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