Problem #1: Can't Use Desktop Chipsets

Although the Pentium M uses the same bus as the Pentium 4, there are two limitations that prevent you from using the Pentium M on regular desktop motherboards or chipsets. The first limitation is that the Pentium M's pin-out is quite different from that of the Pentium 4, despite the similarity in number of pins and socket layout to the Socket-478 Pentium 4s. So, even if the Pentium M could fit in a desktop Pentium 4 board, it still wouldn't work - it's like plugging a USB cable into a FireWire port; even if you could make it fit, you're not going to be transferring anything over that cable.

What about a simple converter that modifies the pin-out of the Pentium M to be compatible with a Pentium 4? The reason why a Pentium M to Pentium 4 converter can't be reliably made is explained by the second limitation: the I/O buffers on the Pentium M operate at relatively low voltages (1.05V) while the I/O buffers on a Pentium 4 operate at the CPU's core voltage (1.3V+). In order to work properly with a Pentium M, the North Bridge (MCH) must be able to operate at similarly low voltages, which none of the current desktop chipsets are able to do. There is also additional drive circuitry that is present on the chipset to help deal with operating at such low voltages, which aren't present on desktop Pentium 4 chips.

The problems resulting from these two limitations are three-fold:
  1. Desktop Pentium M motherboards must use mobile chipsets, which are $10 more expensive on average than their desktop equivalents, leading to more expensive motherboards.
  2. Current desktop Pentium M motherboards are about 6 - 12 months behind the design schedule of mobile Pentium M motherboards, meaning that they are all using Intel's 855GME chipset, unfortunately, and not the latest mobile 915 chipset. The biggest implication here is that this means that all current generation desktop Pentium M motherboards feature only a single channel DDR333 memory controller.
  3. The upgrade path for desktop Pentium M motherboards will be quite limited. The problem is that you're pretty much guaranteed only to be able to upgrade to faster 90nm Dothan based Pentium M processors, which aren't going to get many speed bumps between now and when they are replaced by Yonah (which won't work in current motherboards). Remember that the Pentium M is designed with a clock speed limit in mind and that limit is very low, so don't expect too many speed bumps between now and the end of the year (our roadmaps indicate only one new speed this year, that's all).

Index Problem #2: Total Cost of Ownership
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  • Lupine - Wednesday, February 16, 2005 - link

    I'm surprised at these results. I'm setting up a new Dell Inspiron 9200 (M 725 @ 1.6GHz/400MHz FSB) and it is schooling both my Barton 2500+ @ 2.2GHz and TBred B 1700+ @ 2.2GHz running Stanford's Folding@Home project (600 point proteins: ~37min per frame for the XP boxes compared to ~34min per frame w/ the laptop).

    So, if it is so weak, what is allowing it to process WUs at such a competitive rate? Sure, that is slower than an A64, but competitive w/ most P4 procs.
    Reply
  • fitten - Thursday, February 10, 2005 - link

    Something else to remember about the Banias/Dothan line of chips... Agressive power reduction was the #1 goal of the design process. In a 'normal' chip design, not all pipeline stages are the same length, the clock speed it runs at is the speed of the slowest part of the CPU. Since power usage is directly related to the frequency of the switching gates, the Intel engineers actually deliberately slowed down some parts of the chip to match the target release speeds (or get close to them) to reduce power consumption. This is, perhaps, the main reason why the frequencies don't scale so well as some would want them to scale. Reply
  • Visual - Thursday, February 10, 2005 - link

    here's another thought... when the opterons launched initially at ECC DDR266, there were similar comments like "give it unbuffered DDR400 or higher and stay out of its way" :) well, now that we have that, ok it did improve performance a bit. but not hugely. shouldn't help the dothan significantly more too. Reply
  • Visual - Thursday, February 10, 2005 - link

    I like how AMD got beaten by the P-M :) not because im intel fan, just because this will make things more interesting now.

    don't catch flame from this comment :p its my oppinion

    Funny how you picked the game benchmarks btw, its almost as if you wanted to show the P-M lacking behind the A64... from what I've seen it beats A64 in HL2 and CSS, and that's a game you don't skip usually :) so why now?

    Also looks suspicious how in lots of tests where P-M performs well with the A64 clock-for-clock or beats it, there is almost no difference in the 3800+ and 4000+ results... like if L2 isnt all that important, yet L2 is exactly how everyone explains the P-M success

    Maybe we'll see some 2MB L2 A64 "emergency edition" once Dothan gets a decent desktop chipset, just like what intel did to (try to) save P4 from the A64 :)
    actually i'd be happy if Dothan motivates AMD to develop faster L2 cache or something.

    Knowing Intel, i dont expect they'd even try to match AMD's prices with the P-M... and there's a lot of room for AMD to decreace prices, as they're selling with quite a margin now. So for sure the P-M won't be cost-effective compared to A64, not if you don't care for ultra-low power consumption at least.

    also it doesn't look likely Dothan could scale beyond 2.6GHz on current 90nm tech. by the time it gets there, AMD should've launched the 2.8 FX and most likely 3GHz too. so I have no doubts AMD will keep the lead for quite a while... maybe the race to 65nm will be the next turning point, as it seems its going smooth for intel (at least for P-M)

    anyway, even if AMD is better in absolute performance, pricepoint and (arguably) clock-for-clock, you gotta admit it to the P-M, it does quite a punch. fun times are coming :)
    Reply
  • Zebo - Wednesday, February 09, 2005 - link

    dobwal buy intel if you want mhz, AMD is for performance. Reply
  • dobwal - Wednesday, February 09, 2005 - link

    i wasn't referring to the FX series. Plus you are not understanding the point i was trying to make. Lets take a look at the FX series.

    OPN Model Operating Freq. Package ADAFX55DEI5AS FX55 2600MHz 939-Pin
    ADAFX53DEP5AS FX53 2400MHz 939-Pin
    ADAFX53CEP5AT FX53 2400MHz 940-Pin
    ADAFX51CEP5AT FX51 2200MHz 940-Pin
    ADAFX51CEP5AK FX51 2200MHz 940-Pin

    the first FX51 was release around late third quarter 2003. So in a little over a year the FX series has only increased 400 Mhz. Can you automatically assume that the FX has poor scalability in terms of cpu speed. NO. You know why, because the EE is underperforming and can't touch the FX. AMD has no need to push large scale speed increases out of the FX line, which would do nothing but increase cost with each new stepping it used to boost performance.

    The same goes for the Dothan at 2.26Ghz by the end of 2005. What other cpu offers the same level of performance vs. battery life. So why push for performance except to push sales.

    You simply can't determine the scalabiltiy of a cpu based on its roadmap especially when its the performance leader in its market segment and has no current viable competitor or one in the near future.
    Reply
  • Aileur - Wednesday, February 09, 2005 - link

    Oh and, superpi relies on the fpu to do its calculations, so so much for this fpu is crap trend we have going here.

    http://mod.vr-zone.com.sg/Aopen_i855_review/25sPIm...
    Reply
  • Aileur - Wednesday, February 09, 2005 - link

    Oh and before you start bragging about the better superpi1mb result of the a64
    http://www.akiba-pc.com/DFI_855/d17g_2608_spi1m.gi...

    this is 1 sec better, with 100mhz less, and single channel ram.
    Reply
  • Aileur - Wednesday, February 09, 2005 - link

    Since you seem to like xtremesystems
    http://www.akiba-pc.com/DFI_855/d15g_2435_spi1m.PN...
    also a 1ghz overclock, also on default voltage

    Id like to see how an a64 would perform on a kt266 (if that were possible)

    Give the pentium m time to mature and all those "OMG HAHA YOU CPUZ IS SO HOT LOLOL!!!1111" will be obsoleet.
    Reply
  • Zebo - Wednesday, February 09, 2005 - link

    58 "How long has A64 been stuck on 2.4Ghz."
    ----------------------------------

    There not. 2.6 FX-55 been out for months. More importantly AMD does'nt have to release new chips the way they dominate the benchmarks now. Could they? Hell ya.They got a nice buffer going, New FX's hit 3.0 on stock air. Cheap 90nm's are now hitting 2.7 on default Vcore and air. And by air I mean AMD's cheap all aluminum HS with a itty bitty 15mmx70mm fan, not Prescotts copper core screamers.

    T8000- You're clueless. Maybe it's the heat generated by your prescott making your head woozy, I dunno, but have a look here..1800 Mhz to 2800 Mhz on default Vcore stock fan.
    http://www.xtremesystems.org/forums/showthread.php...
    Reply

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