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Intel's Pentium M on the Desktop - A Viable Alternative?

 by Anand Lal Shimpi on February 7, 2005 4:00 PM EST
77 Comments | Add A Comment
77 Comments

Understanding Pentium M Architecture

There is no doubt that the Pentium M performs very well as a low power, high performance mobile processor. We published two articles comparing the performance of the Pentium M Athlon 64 and Pentium 4, and in both cases the Pentium M did exceptionally well.

The problem is that until recently, the only mobile platforms were all single channel DDR solutions, making it difficult to extrapolate how the Pentium M would fare against its competition in the desktop world. The desktop Pentium 4 and Athlon 64s aren't equipped with a single channel memory controller and they come in larger cache, higher performance models than in the thin and light systems on the mobile side that you find them.

Before we get to the actual performance comparison, there's a lot that needs to be understood about the Pentium M architecture.

While the underlying architecture of the Pentium M is far more complex than this, the real world application performance of the CPU can be summarized and understood when looking at four points:
  1. High IPC Core
  2. Low Latency L2 Cache
  3. Memory Latency and Bandwidth, and
  4. FPU Performance
The high IPC core has already been explained in previous articles on the Pentium M, as well as briefly recapped in this article. With a shorter pipeline than the Pentium 4, but one longer than the Pentium III, the Pentium M can do more per clock than its more popular desktop cousin - which is why it is able to remain competitive despite its lower clock speeds (much like the Athlon 64).

Through the use of technologies like micro-ops fusion and its sophisticated branch prediction unit, the Pentium M ends up being even more efficient per clock than a Pentium III - despite having a longer pipeline. Based on its SPEC CPU2000 scores, the Pentium M features a 20% higher IPC than the Pentium III at an identical clock speed, despite its longer pipeline. The Pentium M vs. Pentium III comparison is similar to the Prescott vs. Northwood comparison, where the deeper pipelined Prescott was still able to make up for the loss in IPC through increases in efficiency and new branch prediction algorithms.

Problem #2: Total Cost of Ownership Low Latency L2 Cache
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  • CSMR - Monday, February 7, 2005 - link

    The fact is it's an excellent processor for business use (speed, quietness, reliability) and multimedia use (quietness). Anandtech is full of gamers; but there is no denying that using a computer as a media centre is becoming a big thing, or that low-power, quiet operation is necessary. High motherboard prices are because the desktop PM motherboard market is very small. There was a comment in the review that the PM architecture doesn't scale well. I am sure that is so; but what processors do scale well? It's because they don't that everyone is about to go dual-core.

  • bobsmith1492 - Monday, February 7, 2005 - link

    Thanks #12 :P

  • Zebo - Monday, February 7, 2005 - link

    I myself have been guilty of hyping dothan after seeing GAMEPCs "opimistic" review. This should quell that.:D

  • Zebo - Monday, February 7, 2005 - link

    Anand best review I've read here, thanks a lot, nice to see you scribing again..:)

    Seems again, like the tech report review, with a comprehensive test suite such as this one dothan has some collosal performance flaws, and simply can't match up the A64 across board. It looses 30 out of 41 benches at same speed, some huge. 2.0 vs 2.0..

    I posted in CPU forum how turion/lancaster will be 25W.. could this be the end of DOTHANS laptop dominace?

  • Brian23 - Monday, February 7, 2005 - link

    I agree with #10.

  • bobsmith1492 - Monday, February 7, 2005 - link

    Sorry; first time commenting. I couldn't remember my login name before.

    Anyway, my laptop OCs better than that. Granted, it's a 1.7 to begin with, but the FSB will do 125 easily, with the same ram increase to boot - 420 MHz, with processor at 2.125. It will do a tad bit more, but that's enough for a laptop I'd say.

  • bobsmith1492 - Monday, February 7, 2005 - link

    test

  • Kalessian - Monday, February 7, 2005 - link

    #6, Oh yeah? Well, give a P4/A64 an SXGP(Super eXtremely Good Performance) setting and stay out of ITS way!

    Yawn, right now the P-M doesn't impress me at all. Let a CPU built for mobile systems stay in mobile systems until it gets rebuilt for desktops properly.

    Great review, learned a ton :)

  • GnomeCop - Monday, February 7, 2005 - link

    I have a 2.0ghz dothan system, I upgraded from an old 533mhz fsb p4.
    The speed for my work and games are just fine. I have a leadtek GF6800ultra in my system and its the only thing I have to worry about cooling.
    CPU is passively cooled and the system is expremely quiet running on a 359watt psu. By the time I need to upgrade, I will be buying a whole new cpu/mobo/everything anyways.

  • ksherman - Monday, February 7, 2005 - link

    seems like an a really good processor for buisness machines, given the L1 cahe speeds... and not much else (snas uber low power consumption)
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