Athlon

Athlon Classic

Athlon Classic launched on June 23, 1999. It showed superior performance compared to the reigning champion, Pentium III, in every benchmark.^[5]

Athlon Classic is AMD's one and only 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.^[6] 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).^[7] 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.^[8]

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, had ample supplies available, causing Athlon sales to become quite strong.

Specifications

• -> K7 "Argon" (250 nm)
• -> K75 "Pluto/Orion" (180 nm)
• L1-Cache: 64 + 64 KiB (Data + Instructions)
• L2-Cache: 512 KiB, external chips on CPU module with 50, 40 or 33% of CPU-speed
• MMX, 3DNow!
• Slot A (EV6)
• Front side bus: 200 MT/s (100 MHz double-pumped)
• VCore: 1.6 V (K7), 1.6 - 1.8 V (K75)
• First release: June 23, 1999 (K7), November 29 1999 (K75)
• Clockrate: 500 - 700 MHz (K7), 550 - 1000 MHz (K75)

Palomino

AMD released the third major Athlon version on October 9, 2001, code-named "Palomino", and named it Athlon XP. The Athlon XP was marketed using a PR rating system, which compared its performance to an Athlon with the "Thunderbird" core. Athlon XP was introduced at speeds between 1333 and 1533 MHz, with ratings from 1500+ to 1800+. At launch, the new core allowed AMD to take the x86 performance lead with the 1800+ model, and enhance that lead with the release of the 1600 MHz 1900+ less than a month later.^[11] The "XP" suffix is interpreted to mean eXtreme Performance and also as an unofficial reference to Windows XP.^[12]

Palomino was the first K7 core to include the full SSE instruction set from the Intel Pentium III as well as AMD's 3DNow! Professional. It is roughly 10% faster than Thunderbird at the same clock speed, thanks in part to the new SIMD functionality and to several additional improvements. The core has enhancements to the K7's TLB architecture and the addition of a hardware data prefetch mechanism to better take advantage of available memory bandwidth.^[13]

Changes in core layout result in Palomino being more frugal with its electrical demands, consuming approximately 20% less power than its predecessor, and thus reducing heat output comparatively as well.^[14] While Athlon "Thunderbird" was near its clock ceiling at 1400 MHz, changes to Palomino's transistor layout and the reduction in power demands allowed it to continue increasing clock speed even at the same 180 nm manufacturing process node and core voltage.

The "Palomino" was actually first released as a mobile version, called the Mobile Athlon 4 (codenamed "Corvette").^[13] Palomino was also available in a form that officially supports dual processing, known as Athlon MP.^[15]

Thoroughbred (T-Bred)

The fourth-generation Athlon, the Thoroughbred, was released 10 June 2002 at 1.8 GHz, or 2200+ on the PR rating system. The "Thoroughbred" core marked AMD's first production 130 nm silicon, resulting in a significant reduction in die size compared to its 180 nm predecessor.

There are two versions of this core, commonly called A and B. The A version was introduced at 1800 MHz, and had some heat and design issues that held its clock scalability back. In fact, AMD wasn't able to increase its clock above Palomino's top grades. Because of this, it was only sold in versions from 1333 to 1800 MHz, replacing the larger Palomino core. The B version of Thoroughbred has an additional metal layer to improve its ability to reach higher clock speeds. It launched at higher clock speeds.

Other than the new manufacturing process, the Thoroughbred design was largely the same as the "Palomino". The Thoroughbred line received an increased front side bus clock during its lifetime, up to 333 MT/s from 266 MT/s. This improved the processor's memory and I/O access efficiency, and improved per-clock performance as a result. AMD shifted their PR rating scheme accordingly, making lower clock speeds equate to higher PR ratings.

Barton and Thorton

Fifth-generation Athlon Barton-core processors released in early 2003 featured PR ratings of 2500+, 2600+, 2800+, 3000+, and 3200+. While not operating at higher clock rates than Thoroughbred-core processors, they earned their higher PR-rating by featuring a total of 512 KiB L2 cache and, in some models, a faster 400 MT/s front side bus.^[16] The Thorton core was a variant of the Barton with half of the L2 cache disabled and thus functionally identical to the Thoroughbred core.

By the time of Barton's release, the "Northwood" Pentium 4 had become more than competitive with AMD's processors.^[17] Unfortunately, due to the architecture of AMD's processor caches, an L2 cache increase to 512 KiB did not have nearly the same impact as it did to Intel's line. Only an increase of several percent was gained in per-clock performance.^[16] The PR rating became somewhat inaccurate because some Barton models with lower clock rate weren't consistently outperforming their higher-clocked Thoroughbred predecessors with lower ratings.^[17]

The other improvement, a higher 400 MT/s bus clock, helped Barton gain some more efficiency. However, it was clear by this time that Intel's quad-pumped bus was scaling well above AMD's double-pumped EV7 bus. The 800 MT/s Pentium 4 bus was well out of Athlon's reach. In order to reach the same bandwidth levels, the Athlon bus would have to be clocked at levels simply unreachable.^[16]

The K7 architecture had scaled to its limit. Maintaining performance equivalence with Intel's improving processors would require a significant redesign.^[16] AMD would soon launch Athlon 64.

Specifications:
Thorton (130 nm)

• L1-Cache: 64 + 64 KiB (Data + Instructions)
• L2-Cache: 256 KiB, fullspeed
• MMX, 3DNow!, SSE
• Socket A (EV6)
• Front side bus: 133/166/200 MHz (266/333/400 MT/s)
• VCore: 1.5 V - 1.65 V
• First release: September 2003
• Clockrate: 1667 - 2200 MHz (2000+ to 3100+)
  • 133 MHz FSB: 1600 - 2133 MHz (2000+ to 2600+)
  • 166 MHz FSB: 2083 MHz (2600+)
  • 200 MHz FSB: 2200 MHz (3100+)

Barton (130 nm)

• L1-Cache: 64 + 64 KiB (Data + Instructions)
• L2-Cache: 512 KiB, fullspeed
• MMX, 3DNow!, SSE
• Socket A (EV6)
• Front side bus: 166/200 MHz (333/400 MT/s)
• VCore: 1.65 V
• First release: February 10, 2003
• Clockrate: 1833 - 2333 MHz (2500+ to 3200+)
  • 166 MHz FSB: 1833 - 2333 MHz (2500+ to 3200+)
  • 200 MHz FSB: 2100, 2200 MHz (3000+, 3200+)

Mobile Athlon XP

Athlon XP Mobile "Barton" 2400+

Mobile Athlon XPs (Athlon XP-M) are identical to normal Athlon XPs, apart from running at lower voltages, often lower bus speeds, and not being multiplier-locked. The lower V_core rating caused the CPU to have lower power consumption (ideal for battery-powered laptops) and lower heat production. Athlon XP-M CPUs also have a higher-rated heat tolerance, a requirement of the tight conditions within a notebook PC.

The Athlon XP-M replaced the older Mobile Athlon 4. The Mobile Athlon 4 used the older Palomino core, while the Athlon XP-M used the newer Thoroughbred and Barton cores. Some specialized low-power Athlon XP-Ms utilize the microPGA socket 563 rather than the standard Socket A.

The CPUs, like their mobile K6+ predecessors, were also capable of dynamic clock adjustment for power optimization. When the system is idle, the CPU clocks itself down through a lower bus multiplier and also reduces its voltage. Then, when a program demands more computational resources, the CPU very quickly (there is some latency) returns to intermediate or maximum speed to meet the demand. This technology was marketed as "PowerNow!". It was similar to Intel's SpeedStep power saving technique. The feature was controlled by the CPU, motherboard BIOS, and operating system. AMD later renamed the technology to Cool'n'Quiet, on their K8-based CPUs (Athlon 64, etc), and re-imagined it for use on desktop PCs as well.

Athlon XP-Ms were popular with desktop overclockers, as well as underclockers. The lower voltage requirement and higher heat rating resulted in CPUs that were basically "cherry picked" from the manufacturing line. Being the best of the cores off the line, the CPUs typically were more reliably overclocked than their desktop-headed counterparts. Also, the fact that they weren't locked to a single multiplier was a significant simplification for the overclocking process. Some Barton core Athlon XP-Ms have been successfully overclocked to as high as 3.1 GHz.

As stated, the chips were also liked for their underclocking ability. Underclocking is a process of determining the lowest V_core at which a CPU can remain stable at for a given clock speed. The Athlon XP-M CPUs were capable of running lower voltages per clock rate compared to their desktop siblings. As such, the chips were used in home theater PC systems due to their high performance and low heat output at low V_core settings.