AMD Athlon XP

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Pros

  • Improved performance
  • lower power consumption
  • still fits into Socket A motherboards
  • supports SSE instructions.

Cons

  • Floating point performance hasn't been improved significantly
  • motherboards with thermal diode support are currently scarce
  • 266MHz frontside bus support only.

AMD has announced the launch of its new XP series of processors, which are based on similar technology to the recent Athlon MP multiprocessor and Athlon 4 mobile chips. Starting with the XP 1500+ (1.33GHz), there are four chips in the initial launch -- we examined one of the top-end XP 1800+ (1.53GHz) models.

Perhaps the first thing to note is the new nomenclature. AMD is trying to move the emphasis away from classifying processors by clock speed. The logic is simple. The amount of work that can be done by a CPU is a function of the work done per clock cycle and the number of clock cycles per unit of time. If an Athlon XP can do more work per cycle, for instance, than a 'Thunderbird' Athlon running at the same clock speed, then to classify their performance simply in terms of gigahertz (i.e. clock speed) would be misleading.

AMD has therefore designed a rating system by running a large number of standard benchmarks (around 35) on Athlon and Athlon XP processors, and named the new products according to the clock speed the existing Athlon would require in order to match the new Athlon XP. In other words, a Thunderbird Athlon would need to run at 1.8GHz (or 1,800MHz) in order to achieve the benchmark results delivered by the XP 1800+, despite the fact that the XP 1800+ actually uses a 1.53GHz (1,533MHz) clock.

This extra performance flows from a number of internal changes, which have been given the marketing handle 'QuantiSpeed Architecture'. What this actually comprises is the inclusion of data as well as instructions in hardware pre-fetch for the cache; support for Intel's SSE instruction set (but not the Pentium 4's SSE2); and a general optimisation of the core design. As well as a performance boost, this results in a 20 per cent reduction in power consumption compared to the Thunderbird design and a resulting drop in operating temperatures -- perhaps the Athlon's weakest point compared to Intel's Pentium 4. Higher operating temperatures require heavier-duty cooling, resulting in increased fan noise.

The new Athlon XPs also have support for internal thermal diodes, allowing for temperature monitoring and shutdown -- this requires motherboard support to operate, though, and compliant motherboards are currently thin on the ground. Other than that, AMD has resisted the temptation to change socket design, so the XP should fit any Socket A motherboard. Unlike Thunderbird Athlons, however, XPs will only operate with a 266MHz frontside bus, so motherboard support will be required for 266MHz chips and older 200MHz-only motherboards will not be able to use the XP.

Other than that, providing a motherboard can support the necessary multipliers (up to 11.5 for the XP1800+), any current Socket A motherboard should be XP-compatible. It may require a BIOS change to support the multiplier, however, so it's best to check with manufacturers' Web sites.

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Performance from the new Athlon XP appears to bear out AMD's claims. As far as overall system performance when running mainstream and high-end applications is concerned, we recorded improvements of 18 and 21 percent respectively compared to a similarly-specified Intel Pentium 4 machine. Tests that examine the CPU/memory subsystem show the 2GHz Pentium 4 out in front. Even when running the workstation-class 3D Studio Max application, which is optimised for the Pentium 4, the Athlon XP came out on top. Both of our Athlon XP 1800+ systems also matched the 2GHz Pentium 4 machine when it came to 3D graphics (see Charts).

AMD has done a good job with the Athlon XP, but the move to 0.13-micron die size is believed to be only a few months away, and Intel's 'Northwood' chips are also nearing release. For the moment, however, the Athlon XP offers AMD users a relatively painless performance upgrade without the need for any other change in system hardware. However, bear in mind that processor improvements do not necessarily lead to improvements in overall system performance.

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