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AMD's Athlon XP 1800+ processor

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TODAY AMD UNLEASHES its new Athlon XP processor on an unsuspecting world. AMD's Athlon processor gets a new name, a revamped design, a new look, and a controversial new marketing scheme. The Athlon XP is AMD's attempt to win back the PC processor performance crown from Intel, whose 2GHz Pentium 4 just edged out the 1.4GHz Athlon in our last round of tests. This new Athlon XP chip runs at only 1.53GHz, but it's likely to take Intel's 2GHz wonder to the woodshed. Read on to find out why.

Palomino finally gallops onto the desktop
The Athlon XP is a revised version of the Athlon based on a core design code-named "Palomino." We've seen Palomino previews in a number of places—in laptop CPUs, in the Athlon MP server/workstation chips, and in little brother "Morgan"—but the Athlon XP is the first Pally aimed at the desktop.

The Palomino core packs in a number of enhancements designed to improve the Athlon's performance, and scalability. Among them:

  • Lower power requirements — Thanks to some changes in the way the chip is made, the Palomino requires about 20% less power than corresponding Thunderbird chips. As you might expect, that means the Palomino runs quite a bit cooler than the T-bird, as well. (For this reason, the Palomino first hit the market as a mobile processor for notebook computers, in the form of the oddly named "Athlon 4" processor.)

    Despite the changes, the Palomino is still made on the same 0.18-micron copper fab process as current Athlons. Intel will soon deliver a die-shrunk Pentium 4, but it will take a while for AMD to make the conversion to 0.13 microns. AMD likes to point out that even a 0.13-micron Pentium 4 has a larger die size than a 0.18-micron Athlon XP.

  • An on-chip thermal diode — Like Intel's Pentium III and 4 processors, the Palomino core includes an on-chip thermal diode for temperature monitoring and better power management.

  • Hardware pre-fetch — Performance-wise, this may be the most important addition to the Palomino. The hardware pre-fetch logic attempts to anticipate what data will be needed from main memory next and preemptively loads this data into the processor's L1 cache. This enhancement, which is similar to logic present in Intel's Pentium 4 and Pentium III "Tualatin" processors, should allow the Athlon to take better advantage of the extra memory bandwidth available with advanced forms of memory like DDR SDRAM.

  • Improved translation look-aside buffers (TLB) — Though more esoteric than hardware pre-fetch, improved TLBs ought to complement data pre-fetch logic nicely. The Palomino's revamped TLB structures are now larger, speculative (as one would expect, with hardware pre-fetch now in the picture), and exclusive (no longer shared) between caches. These improved TLBs should help keep the Athlon's pipeline fed, increasing clock-for-clock performance.

  • SSE compatibility — AMD says the Palomino includes 52 new instructions that comprise something called "3DNow! Professional." These instructions just happen to correspond to the instructions the original Athlon needed in order to be compatible with Intel's SSE, or streaming SIMD extensions. These extra instructions do not provide compatibility with the Pentium 4's new SSE2 instructions, but they should yield improved performance in applications optimized for SSE but not for AMD's competing 3DNow! extensions.

  • More transistors — To accommodate these new features, the Palomino weighs in at about half a million more transistors than the Athlon Thunderbird, up from 37 million to 37.5 million.
Cumulatively, these improvements should make the Athlon XP quite a bit better than its predecessor. The T-bird had no significant performance weaknesses to speak of, except that it wasn't entirely able to make use of the extra bandwidth provided by DDR memory. Palomino ought to remedy that weakness and add some new strengths.