In early 2002 it became known that the AMD had working samples of the sucessor of the Athlon XP, the new ClawHammer CPU's. It wasn't until late 2002 for early benchmarks to leak out. ClawHammer made it's debut at 22 April 2003 in the form of an Opteron. At 23 September 2003 the Athlon 64 was launched. Read the story of the Athlon HX 1400 which is a early Athlon 64 from May 2002.

ClawHammer is made at 130nm, just like the last iteration of Athlon XP's. It has an on-die memory controller which runs at the same clock as the CPU and has a shorter path to the memory. The shorter path results in a lower latency which makes the system faster. Several changes have been made to improve branch prediction, reduce latencies and improve SSE-instructions.

The new ClawHammer also features Cool 'n Quiet; a technique like Intel SpeedStep which lowers the clock-frequency when the CPU is idle. Todays CPU use this technique as well but back in 2002/2003 it was new. AMD also used a heatspreader to protect the vulnerable processor core.

AMD also uses a HyperTransport bus as 'front-side-bus'. The HyperTransport bus is faster and works pretty well with 2-way and 4-way multiprocessor systems. 4-way systems were only available for SledgeHammer cores, which are basically identical to ClawHammer but with 1MB L2-cache rather than 512KB

At last but not least: this is AMD's first 64-bit processor. It's not a new architecture (like Intel IA-64 for Itanium systems) but an evolution of the x86 architecture. Often the term x86-64 was used but later on people referred to AMD64. Intel also implemented x86-64 instructions which they called Intel EM64T (often mispelled as EMT64) but later renamed it to Intel 64.