Last night saw the launch of AMD's 64bit processor, the Athlon 64, aka Clawhammer, the first aimed at mainstream desktop PC users.

AMD has launched two 64bit processors: the high-end 2.2GHz Athlon 64 FX-51, and the consumer-level 2GHz Athlon 64 3200+. The two Athlon 64s sit in different sockets; the Athlon 64 3200+ in a Socket 754 and the FX-51 in a Socket 940, the difference being that the former supports a single memory channel, while the latter has the pins to support dual memory channels.

The Athlon 64 can operate in one of three modes: 32bit 'legacy' (aka 'Intel') mode; dual 32/64bit 'compatibility' mode and pure 64bit (x86-64 AMD) mode. The last two require a 64bit operating system, and are essentially sub-modes of the chip's 64bit 'long' mode. The ability to run 32bit code without a speed penalty is a major plus for the Athlon 64.

The Athlon 64 will give consumer desktops access to one terabyte of memory ? more than the 4GB the limit on 32bit computers. The new CPUs feature 1MB of L2 cache ? double that of the Athlon XP 3200+ ? better branch prediction algorithms and bigger TLB (translation look-aside buffers), all of which will make Athlon 64 run faster than an Athlon XP working at the same clock frequency.

A major innovation feature is an integral DDR SDRAM controller, which will reduce latencies on data requests. The CPU and the South Bridge will be connected with the Hyper Transport bus, with up to 3.2GBps (gigabytes per second) bandwidth in each direction.

Although the initial Athlon 64s have a performance rating of 3200+ they are slated to reach a performance point of 3700+ during early 2004, rising to 4300+ by the end of the year.

The big problem facing the Athlon 64 is that the average PC user doesn't actually need 64bits just yet. Indeed, cutting-edge PCs still ship with just 1GB of RAM ? far from the 4GB ceiling imposed by 32bit processors. Gamers or those who use complex programs like CAD, may benefit but most ordinary users will see the Athlon 64 as a faster iteration of the 32bit Athlon XP.

To read our review of one of two of the first Althon 64-based systems, click here.

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