Product Reviews

AMD released its dual-core processor, the Athlon 64 X2, last month as we were going to press. We printed our initial findings then, but this month we've tested the processor in greater detail.

We were provided with an X2 4800+ processor, an Asus nForce 4 SLI motherboard and 512MB of RAM in a dual-channel configuration. As with other AMD chips, the model name is based on the company's Performance Rating (PR). This basically shows that it performs as well as a processor running at 4.8GHz.

Like Intel's dual-core processor, which we reviewed in What's New, Shopper July 2005, the X2 4800+ has two processor cores in one package. In the case of the X2 4800+, both run at 2.4GHz, the same speed as the Athlon 64 4000+. Essentially, you get two Athlon 64 4000+ processors in a single chip.

As the Athlon 64 uses AMD's HyperTransport, the X2 4800+ has an integrated memory controller, which both cores can access. This provides a more efficient and faster mechanism for accessing memory than relying on a Northbridge motherboard chip, as Intel's processor does.

Manufacturing two cores in a single processor is cheaper than making two separate processors, and the motherboards are also cheaper as they need only a single socket. As Microsoft licenses Windows on a per-socket basis, there's also no additional cost for the operating system. In the case of the Athlon 64 X2 range, the chip should work on any Socket 939 motherboard, although you might need to update the BIOS first. This is significantly better than Intel's approach, which requires you to buy a new motherboard with either the 945, 955, or nVidia nForce 4 chipset.

While the processor name gives an indication of performance, in this case it's slightly misleading

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as judging the performance of this processor isn't a straightforward matter. For an application to take advantage of both cores it has to be multithreaded. A thread is an independent part of an application, usually an individual task. For example, in a video-editing application each thread might apply an effect. Having two cores on a processor means that two threads can be executed simultaneously, improving performance.

However, hardly any software is multithreaded at the moment, so the two cores can't be used to their full extent. As most software uses a single core, the X2 4800+ performs much like a standard Athlon 64 4000+. However, when you run two applications simultaneously, each one has access to a physical processor, so both applications run at high speed. With single-core processors, multiple applications have to share a single processor. The end result is that one application grabs the lion's share of the processor time to the detriment of the second application.

As both the X2 4800+'s cores are 64-bit the chip offers the potential for better performance once 64-bit applications are more widely available. As it stands, only the operating system (Windows XP Professional x64 edition) takes advantage of this - see our Windows XP 64-bit feature in Shopper July 2005 for more details.

Running PCMark04's processor test, which uses multithreaded content, the X2 4800+ scored 6,538 compared to the Athlon 64 4000+'s 4,446. It's the highest processor score we've ever seen. For a full breakdown on how the X2 4800+ compares against a single-core Athlon 64 4000+.

The X2 4800+ costs the same as Intel's Pentium 4 Extreme Edition 840. However, due to its Hyper-Threading technology, which presents Windows with four processors, the 840 scored higher in our application benchmarks. This marks it as the slightly better product in our opinion.

That said, to use Intel's 840 you'll have to buy a new motherboard. If you already have a Socket-939 board, it's highly likely that you'll be able to upgrade to an AMD dual-core system now. Before you rush out, though, bear in mind that it's only worth doing if you already run multithreaded applications or you need to run two applications at once. If neither applies, you'd be better off spending your money on the fastest single-core processor you can afford.