Athlon

Athlon is the generic name applied to 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 the first non-Intel processor to be the long-durationly unchallenged all-aspect mainstream performance-leader in almost 20 years.

Athlon Classic

The Athlon made its debut on August 21, 1999. The name "Athlon" was chose by AMD as short for "decathlon", which the company thought was an appropriate name for its high-performance processor. The original Athlon core revision, code-named "K7" (in homage to its predacessor, the K6), was available in speeds of 500 to 650 MHz at its introduction and was later sold at speeds up to 1000 MHz. The processor was compatible with the industry-standard X86 instruction set and plugged into a motherboard slot mechcanically similar to but not functionally 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 512k of secondary cache, 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 less than this (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 particlar, Intel's transition to a 0.18 micron 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 avalable, and Athlon sales went from strength to strength.

Athlon Thunderbird

The second-generation Athlon, the Thunderbird, debuted on June 4, 2000. This version of the Athlon shipped in a less clumsy and 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 512k external reduced-speed cache of the Athlon Classic with 256K 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 386DX-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 big 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 mainboard speed to 266MHz and providing roughly 10% extra performance over the "A" model Thunderbird.

Athlon XP

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Athlon XP 2100 Thoroughbred.

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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 1.7GHz P4 (April 2001) served notice that the Thunderbird could not count on retaining performance leadership forever, but thermal and electricity-consumption issues with the Thunderbird design meant that it wasn't practical to take it past 1400MHz.

AMD released the third major Athlon version on May 14, 2001, code-named "Palomino". This version, the first to include the SSE instuction set from the Intel Pentium III as well as AMD's 3DNow, was introduced at speeds between 1333 and 1733 MHz. The major changes were optimisations to the core design to increase efficiency by roughly 10% over a Thunderbird at the same clockspeed, and power consumption reductions to allow it to be clocked faster.

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.

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 1933 MHz and the 2600+ running at 2066 MHz, were announced on August 21. 2700+ and 2800+ Thoroughbred-core parts were also announced, but became available in insiginificantly small quantities.

Fifth-generation Athlon Barton-core parts released in early 2003 featured PR ratings of 2500+, 2600+, 2800+ and 3000+. While not faster than Thoroughbred-core processors in megaburtz terms, they earned their higher PR-rating-per-megahurt from featuring additional speed-increasive on-chip cache ram.

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 test 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 in the world, believing that that Intel's Pentium 4 overtook the Athlon XP early in 2002 and held its until February 2003, with the 3.06 GHz P4 benchmarking slighly faster than the Athlon 2700+. At the time, the question was moot: AMD had yet to deliver the 2700+ and 2800+ in commercial quanties; 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 micron process neared completion, AMD began producing large numbers of 0.13 micron 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+ has according to AMD reclaimed the "fastest X86 in the world" title for the Athlon once again. However reviewers' opinions on this are split, with most believing the top Intel part to still be faster.

Future versions of the Athlon will be based on the 64-bit x86-64 "Hammer" technology, and are expected to debut in the second half of 2003.

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This article contains some material from the "K7" article from FOLDOC, used with permission.