The Athlon 64 X2 is the same size as current single-core Athlon 64 CPUs, and does not require any new hardware--it will (theoretically) work on any Athlon 64 motherboard that has a 939-pin socket. However, some motherboards need a BIOS upgrade to provide full support for the X2. That's good news for those of us who already have a 939-pin setup, as we can make a significant CPU upgrade without forking out for a new motherboard.

The X2 retains all the features that have made the Athlon 64 such a popular CPU among performance seekers and enthusiasts. It has 64-bit processing, of course, as well as an integrated dual-channel DDR memory controller, Hyper-Transport technology, Cool'n'Quiet Technology, and SSE3 multimedia instructions (for applications that support them).

The two CPU cores in the X2 sit on the same piece of silicon, so they can "talk" to each other at full speed. They both have access to the memory controller in the CPU as well as the Hyper-Transport link.

Data requests are sent from these to the CPUs using a system request interface, which directs data to the CPU that requires it. Each CPU has its own Level 2 cache memory (size depending on the model you buy).

Initially, the X2 models available are the 4200+, 4400+, 4600+ and the 4800+. The 4200+ runs at 2.2GHz and has a 512KB cache; the 4400+ runs at 2.2GHz and has a 1MB cache. The 4600+ runs at 2.4GHz and has a 512KB cache; and the 4800+ runs at 2.4GHz and has a 1MB cache.

We tested the 4800+, and it achieved a record score (at the time of writing) of 109 in PC WorldBench 5 and was particularly strong in multitasking, Windows Media Encoder, Adobe Premiere and Photoshop tests.