The Athlon 64 is a ninth-generation, AMD64-architecture microprocessor produced by Advanced Micro Devices (AMD), released on September 23, 2003.

It was AMD's primary consumer CPU, and primarily competed with Intel's Pentium 4, especially the Prescott and Cedar Mill core revisions.

[6] Like the Opteron, on which it was based, the Athlon FX-51 required buffered random-access memory (RAM), increasing the final cost of an upgrade.

[9] Despite a very strong demand for the chip, AMD experienced early manufacturing difficulties that made it difficult to deliver Athlon 64s in quantity.

[11] The Athlon FX-51 also outperforming the Pentium 4 3.2C in Quake III Arena and Unreal Tournament 2003 benchmark, according to Maximum PC.

[18] San Diego, the higher-end chip, was produced only for Socket 939 and doubled Venice's L2 cache to 1 MB.

[22] In addition, AMD overhauled the memory controller for this revision, resulting in performance improvements as well as support for newer DDR SDRAM.

[27] The Athlon 64 X2 was received very well by reviewers and the general public, with a general consensus emerging that AMD's implementation of multi-core was superior to that of the competing Pentium D.[28][29] Some felt initially that the X2 would cause market confusion with regard to price points since the new processor was targeted at the same "enthusiast," US$350 and above market[30] already occupied by AMD's existing socket 939 Athlon 64s.

[31] AMD's official breakdown of the chips placed the Athlon X2 aimed at a segment they called the "prosumer", along with digital media fans.

[34] AMD's official position was that the CAS latency on DDR2 had not progressed to a point where it would be advantageous for the consumer to adopt it.

[35] AMD finally remedied this gap with the "Orleans" core revision, the first Athlon 64 to fit Socket AM2, released on May 23, 2006.

Based on the same architecture as the other Athlon 64 variants, the new processor features a small package footprint targeting Ultra-portable notebook market.

[42] All Athlon 64s also support the NX bit, a security feature named "Enhanced Virus Protection" by AMD.

This means the controller runs at the same clock rate as the CPU, and that the electrical signals have a shorter physical distance to travel compared to the old northbridge interfaces.

[45] The result is a significant reduction in latency (response time) for access requests to main memory.

[44] This and other architectural enhancements, especially as regards SSE implementation, improve instructions per cycle (|IPC) performance over the prior Athlon XP generation.

With prior AMD CPUs, a CPU shim could be used by people worried about damaging the die.

The No Execute bit (NX bit) supported by Windows XP Service Pack 2 and future versions of Windows, Linux 2.6.8 and higher and FreeBSD 5.3 and higher is also included, for improved protection from malicious buffer overflow security threats.

[59] From FX-70 onwards, the line of processors will also support dual-processor setup with NUMA, named AMD Quad FX platform.

They are equipped with 512 or 1024 kB of L2 cache, a 64-bit single channel on-die memory controller, and an 800 MHz HyperTransport bus.

The clock of the processors is significantly lower than desktop and other mobile counterparts to reach a low TDP, at 15W maximum for a single core x86-64 CPU at 1.6 GHz.

The Athlon Neo processors are equipped with 512 kB of L2 cache and HyperTransport 1.0 running at 800 MHz frequency.

The onboard memory controller was not capable of running unbuffered (non-registered) memory in dual-channel mode at the time of release; as a stopgap measure, they introduced the Athlon 64 on Socket 754, and brought out a non-multiprocessor version of the Opteron called the Athlon 64 FX, as a multiplier unlocked enthusiast part for Socket 940, comparable to Intel's Pentium 4 Extreme Edition for the high end market.

In August 2006, AMD released Socket F for Opteron server CPU which uses the LGA chip form factor.