Athlon is the brand name applied to a series of different x86 processors designed and manufactured by AMD. The original Athlon, or Athlon Classic was the first seventh-generation x86 processor and, in a first, retained the initial performance lead it had over Intel's competing processors for a significant period of time. AMD has continued the Athlon name with the Athlon 64, an eighth-generation processor featuring AMD64 technology.
The Athlon made its debut on August 21, 1999. The name "Athlon" was chosen by AMD as short for "decathlon." The original Athlon core revision, code-named "K7" (in homage to its predecessor, the K6), was available in speeds of 500 to 650 MHz at its introduction and was later sold at speeds up to 1000 MHz (K75). The processor was compatible with the industry-standard X86 instruction set and plugged into a motherboard slot mechanically similar to but not pin-compatible with the Pentium II's Slot 1.
Internally, the Athlon was essentially a major reworking of the K6 processor core designed for compatibility with the EV6 bus protocol (first used on DEC's Alpha 21264 RISC processor). AMD dramatically improved the floating-point unit from the K6 and put a large 128K level 1 cache on the chip. Like Intel's Pentium II and Katmai Pentium III, there was a secondary cache of 512K, mounted externally to the chip itself but still within the CPU module, and running at a lower speed than the core: initially half-speed, but later runs at 1/3 to 2/5 of the core speed (because of cost and availability issues with very high speed cache RAM).
The resulting processor was the fastest x86 in the world. Various different versions of the Athlon held this distinction continuously from August 1999 until January 2002.
In commercial terms, the Athlon Classic was an enormous success - not just because of its own merits, but also because the normally dependable Intel endured a series of major production, design, and quality control issues at this time. In particular, Intel's transition to a 0.18 μm production process, starting in late 1999 and running through to mid-2000, was chaotic, and there was a severe shortage of Pentium III parts. Many long-time Intel-only PC dealers found the combination of the Athlon's excellent performance and reasonable pricing tempting, and the prospect of being able to get stock in commercial volumes impossible to resist. In contrast, AMD enjoyed a remarkably smooth process transition, had ample supplies available, and Athlon sales went from strength to strength.
The second-generation Athlon, the Thunderbird, debuted on June 4, 2000. This version of the Athlon shipped in a more traditional pin-grid array (PGA) format that plugged into a socket ("Socket A") on the motherboard. It was sold at speeds ranging from 700 to 1400 MHz. The major difference, however, was cache design. Just as Intel had done when they replaced the old Katmai Pentium III with the much faster Coppermine P-III, AMD replaced the 512 K external reduced-speed cache of the Athlon Classic with 256 K of on-chip, full-speed cache. (As a general rule, more cache improves performance, but faster cache improves it further still.)
The Thunderbird was AMD's most successful part since the Am386DX-40 ten years earlier. Mainboard designs had improved considerably by this time, and the initial trickle of Athlon mainboard makers has swollen to include every major manufacturer. Their new fab in Dresden came on-line, allowing further production increases, and the process technology was improved by a switch to copper interconnects. In October 2000 the Athlon "C" was introduced, raising the mainboard front side bus speed to 133 MHz (allowing for DDR266) and providing roughly 10 % extra performance over the "A" model Thunderbird.
In performance terms, the Thunderbird had easily eclipsed the rival Pentium III, and the early Pentium 4s were a long way off the pace, but gradually clawed their way closer. The 1.7 GHz P4 (April 2001) served notice that the Thunderbird could not count on retaining performance leadership forever, and thermal and electricity-consumption issues with the Thunderbird design meant that it wasn't practical to take it past 1400 MHz (even that speed thermally marginal).
AMD released the third major Athlon version on May 14, 2001, code-named "Palomino". This version, the first to include the SSE instruction set from the Intel Pentium III as well as AMD's 3DNow! Professional, was introduced at speeds between 1333 and 1733 MHz. The major changes were optimizations to the core design to increase efficiency by roughly 10 % over a Thunderbird at the same clock-speed, and power consumption reductions to allow it to be clocked faster.
The "Palomino" did have one major flaw, however: it ran very hot. Its SMP enabled version, the Athlon MP entry (which was the first to carry the Palomino core, not the Athlon XP), was initially hammered due to heat issues with the Palomino core.
The Athlon XP was marketed using a PR rating system, which compared its performance to an Athlon Thunderbird. Because the Athlon XP has much higher IPC (instructions per clock) than the Pentium 4 (and about 10 % higher than a Thunderbird), it is more efficient and delivers the same level of performance at a lower clock-speed, or higher performance at the same speed.
Athlon XP 2100 Thoroughbred
The fourth-generation Athlon, the Thoroughbred core, was released June 10, 2002 at 1.8 GHz, or 2200+ on the PR rating system. Two new Athlon XP's, the 2400+ running at 2000 MHz and the 2600+ running at 2083 MHz (or 2133 MHz when for 133/266 MHz front side bus), were announced on August 21. 2700+ and 2800+ Thoroughbred-core parts were also announced, but became available in insignificantly small quantities.
The "Thoroughbred" core was on a 0.13 micrometre process, unlike the 0.18 micrometre process of its "Palomino" predecessor. Other than the micrometre process, the Thoroughbred design was not different from the "Palomino" in any way. AMD did have initial troubles with the "Thoroughbred A" revision having substantial heat issues, which were solved in the "B" revision. The rev. A may have been on the 130 nm process, but it offered no real improvements over the old Palomino. Over clockers still liked to use the Palomino, even with it being made on the 180 nm process it still was able to hit higher clock speeds. The Thoroughbred "B" fixed this problem. AMD was able to hit speeds that would allow them to over take the market again. AMD was able to produce 2600+ at first to help them take the market from Intel. Later, AMD raised the FSB from 133 (266) to 166 (333). This allowed AMD to produce processors up to 2800+ speeds that had much power. AMD however was unable to release 2800+ processors in very large shipments and most were unable to get them. The 2700+, now, can be found with little trouble.
Barton and Thorton
Fifth-generation Athlon Barton-core parts released in early 2003 featured PR ratings of 2500+, 2600+, 2800+, 3000+, and 3200+. While not faster than Thoroughbred-core processors in megahertz terms, they earned their higher PR-rating-per-megahertz from featuring an additional 256K of full-speed on-chip level 2 cache and a faster FSB. The Thorton core is a variant of the Barton with half of the L2 cache disabled and thus is functionally identical to the Thoroughbred B core. Some Thortons could have the disabled L2 cache re-enabled through bridge modifications.  (http://www.xbitlabs.com/news/cpu/display/20030930171549.html)
Some AMD proponents claim that these new parts regained performance leadership for the Athlon, but this remained in doubt. Much controversy surrounds the benchmarks which are used to measure performance leadership. In particular, industry insiders point out that some tests have been deliberately skewed in Intel's favour - notably the BAPCo tests, which were written by Intel's own engineers.
Most observers considered that the Athlon was no longer the fastest x86 processor in the world, believing that Intel's Pentium 4 overtook the Athlon XP early in 2002 and held its lead until February 2003, with the 3.06 GHz P4 benchmarking slightly faster than the Athlon 2700+. At the time, the question was moot: AMD had yet to deliver the 2700+ and 2800+ in commercial quantities; they did not begin to ship in volume until well into the first quarter of 2003. However, as the initially troublesome transition to the 0.13 micrometre process neared completion, AMD began producing large numbers of 0.13 micrometre parts in the 1700 to 2400 speed grades (usually a sign that faster grades are not far away) and, in mid February 2003, announced the Athlon XP 3000+ to ship in volume in early March of 2003. Pending an Intel reply, the 3000+ had according to AMD reclaimed the "fastest x86 in the world" title for the Athlon once again. However reviewers' opinions on this were split, with most believing the top Intel part to still be faster.
Mobile Athlon XP
Mobile Athlon XPs (Athlon XP-M) are functionally identical to normal Athlon XPs, apart from running at lower voltages and not being multiplier-locked. The lower vcore ratings allow the CPU to run with less electricity consumption (ideal for battery-powered laptops) and produce less heat. They're also capable of having their multipliers and bus speeds intelligently adjusted by software for the needs of processing power.
It also features Power Now! where the CPU's clock speed is automatically decreased when the computer is under a low load, to save battery power and reduce heat. Similar to Intel's SpeedStep technology.
Some specialized low-power Athlon XP-Ms utilise the -PGA socket rather than the standard Socket A.
Due to their lack of multiplier locking, the use of Athlon XP-Ms on desktop computers became very popular with overclockers as well as underclockers by early 2004. Some Barton core Athlon XP-M 2600+s have been successfully overclocked to as high as 3.1 GHz.
Mobile Athlon XPs are also attractive CPUs for use in home theater systems due to their high performance and ability to underclock & undervolt for quiet operation needed in the living room.
- Main Article : Athlon 64
Athlon 64 is based on the 64-bit x86-64 (now known as AMD64) "Hammer" technology. This is the home consumer version of the Opteron chip, both belonging to the AMD64 family. There are two variants: Athlon 64 and Athlon 64 FX. The Athlon 64 FX is similar to the Opteron and more powerful than the standard Athlon 64. Athlon 64 runs 16 bit, 32 bit, and AMD's own 64 bit assembly code. Currently, Linux, FreeBSD, OpenBSD and NetBSD support the 64-bit mode of Athlon 64, and Microsoft has released betas of Windows XP and Windows Server 2003 with 64-bit support.
Athlon 64 also features CPU speed throttling technology (similar to the Athlon XP-M) branded Cool 'n' Quiet. When the user is running undemanding applications and the load on the processor is light, the processor's clock speed and voltage are reduced. This in turn reduces its peak power consumption from 89W to as low as 32W (C0 revision) or 22W (CG revision).
The Athlon 64 put AMD back in the high-end processor production again. The FX-55 is able to hold its own with compared to a Pentium 4 EE at 3.4 GHz and the 3.6 GHz Prescott. Even with DDR2 memory on the Pentium 4's side AMD is still able to pack a hard punch, mainly with the design of the processor. The onboard memory controller allows the Northbridge to be removed from the motherboard. The Athlon 64 seems to scale pretty well. Dual-channel memory on socket 939 allows for the L2 to be cut back to 512K and give very good power. AMD plans to make mainly processors with 512K since it costs less and is easier to make. The Athlon FX will have 1024K of L2 for a while longer.
With the Athlon 64, AMD has managed to take over the lead from Intel in terms of speed and technology.
Athlon 64 FX
Like Opteron, Athlon 64 FX is based on the same core code-named Sledgehammer, because of this, first FX processors used same Socket 940 and required registered memory, like their server counterparts. Later, Socket 939 was introduced, which used unbuffered memory and no longer required registered memory. Athlon 64 FX processors are aimed at high-end market and are positioned against Intel's Pentium 4 Extreme Edition CPUs. AMD does not use frequency or performance ratings to identify their FX CPUs, instead model numbers are used. So far three Athlon 64 FX models have been released: FX-51 (2.2 GHz), FX-53 (2.4 GHz), and FX-55 (2.6 GHz). However, AMD makes sure that only one FX model is on market: as soon as new FX model is introduced, the older model is phased out. Athlon 64 FX processors differ from other Athlon 64 processors by having both 1MB L2 cache and 128-bit dual channel memory interface.
With the FX-55 replacing the FX-53, a new Athlon 64 4000+ hit the market. But the 4000+'s core is the same as the FX-53, unlike the rest of the non-FX Athlon 64s. The only difference is that the 4000+'s multiplier is locked, unlike the FX-53's, which allowed for easier overclocking.
Mobile Athlon 64
This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.