my computer's room: AMD Athlon

AMD Processor

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 (later renamed x86-64) technology.

The Athlon made its debut on June 23, 1999. The name was chosen by AMD as short for "decathlon". Athlon was the ancient Greek word for "Champion/trophy of the games".

AMD ex-CEO and founder Jerry Sanders developed strategic partnerships during the late 1990s to improve AMD's presence in the PC market based on the success of the K6 architecture. One major partnership announced in 1998 paired AMD with semiconductor giant Motorola. In the announcement, Sanders referred to the partnership as creating a "virtual gorilla" that would enable AMD to compete with Intel on fabrication capacity while limiting AMD's financial outlay for new facilities. This partnership also helped to co-develop copper-based semiconductor technology, which would become a cornerstone of the K7 production process.

In August 1999, AMD released the Athlon (K7) processor. Notably, the design team was led by Dirk Meyer, one of the lead engineers on the DEC Alpha project. Jerry Sanders had approached many of the engineering staff to work for AMD as DEC wound the project down, and brought in a near-complete team of engineering experts. The balance of the Athlon design team was comprised of AMD K5 and K6 veterans.

By working with Motorola, AMD was able to refine copper interconnect manufacturing to the production stage about one year before Intel. The revised process permitted 180-nanometer processor production. The accompanying die-shrink resulted in lower power consumption, permitting AMD to increase Athlon clock-speeds to the 1 gigahertz range . AMD found processor yields on the new process exceeded expectations, and delivered high speed chips in volume in March 2000.

Internally, the Athlon is a fully seventh generation x86 processor, the first of its kind. Like the AMD K5 and K6, the Athlon is a RISC microprocessor which decodes x86 instructions into its own internal instructions at runtime. The CPU is an out-of-order design, again like previous post-5x86 AMD CPUs. The Athlon utilizes the DEC Alpha EV6 bus architecture with double data rate (DDR) technology. This means that at 100 MHz the Athlon front side bus actually transfers at a rate similar to a 200 MHz single data rate bus (referred to as 200 MT/s), which was superior to the method used on Intel's Pentium III (with SDR bus speeds of 100 and 133MHz).

AMD designed the CPU with more robust x86 instruction decoding capabilities than that of K6, to enhance its ability to keep more data in-flight at once. Athlon's CISC to RISC decoder triplet could potentially decode 6 x86 operations per clock, although this was somewhat unlikely in real-world use. The critical branch predictor unit, essential to keeping the pipeline busy, was enhanced compared to what was onboard the K6. Deeper pipelining with more stages allowed higher clock speeds to be attained. Whereas the AMD K6-III+ topped out at 570 MHz due to its short pipeline, even when built on the 180 nm process, the Athlon was capable of going much higher.

AMD ended its long-time handicap with floating point x87 performance by designing an impressive super-pipelined, out-of-order, triple-issue floating point unit. Each of its 3 units were tailored to be able to calculate an optimal type of instructions with some redundancy. By having separate units, it was possible to operate on more than one floating point instruction at once. This FPU was a huge step forward for AMD. While the K6 FPU had looked anemic compared to the Intel P6 FPU, with Athlon this was no longer the case.

The 3DNow! floating point SIMD technology, again present, received some revisions and a name change to "Enhanced 3DNow!". Additions included DSP instructions and an implementation of the extended-MMX subset of Intel SSE.

CPU Caching onboard Athlon consisted of the typical two levels. Athlon was the first x86 processor with a 128 KiB split level 1 cache; a 2-way associative, later 16-way, cache separated into 2×64 KiB for data and instructions (Harvard architecture). This cache was double the size of K6's already large 2×32 KiB cache, and quadruple the size of Pentium II and III's 2×16 KiB L1 cache. The initial Athlon (Slot A, later renamed Athlon Classic) used 512 KiB of level 2 cache separate from the CPU, on the processor cartridge board, running at 50% to 33% of core speed. This was done because the 250 nm manufacturing processes was too large to allow for on-die cache while maintaining cost-effective die size. Later Athlon CPUs, afforded greater transistor budgets by smaller 180 nm and 130 nm process nodes, moved to on-die L2 cache at full CPU clock speed.

Athlon Classic launched on June 23, 1999. It showed superior performance compared to the reigning champion, Pentium III, in every benchmark.

Athlon Classic is a cartridge-based processor. The design, called Slot A, was quite similar to but incompatible with Intel's Slot 1 cartridge used for Pentium II and Pentium III. The cartridge allowed use of higher speed cache memory than is possible to put on the motherboard. Like Pentium II and the "Katmai"-core Pentium III, Athlon Classic used a 512 KiB secondary cache. This cache, again like its competitors, ran at a fraction of the core clock rate and had its own 64-bit bus, called a "backside bus" that allowed concurrent system front side bus and cache accesses. Initially the L2 cache was set for half of the CPU clock speed, on up to 700 MHz Athlon CPUs. Faster Slot-A processors were forced to compromise with cache clock speed and ran at 2/5 (up to 850 MHz) or 1/3 (up to 1 GHz). The SRAM available at the time was incapable of matching the Athlon's clock scalability, due both to cache chip technology limitations and electrical/cache latency complications of running an external cache at such a high speed.

The Slot-A Athlons were the first multiplier-locked CPUs from AMD. This was partly done to hinder CPU remarking being done by questionable resellers around the globe. AMD's older CPUs could simply be set to run at whatever clock speed the user chose on the motherboard, making it trivial to relabel a CPU and sell it as a faster grade than it was originally intended. These relabeled CPUs were not always stable, being overclocked and not tested properly, and this was damaging to AMD's reputation. Although the Athlon was multiplier locked, crafty enthusiasts eventually discovered that a connector on the PCB of the cartridge could control the multiplier. Eventually a product called the "Goldfingers device" was created that could unlock the CPU, named after the gold connector pads on the processor board that it attached to.

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 the 180 nm production process, starting in late 1999 and running through to mid-2000, suffered delays. There was a shortage of Pentium III parts. In contrast, AMD enjoyed a remarkably smooth process transition and had ample supplies available, causing Athlon sales to become quite strong.

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