Intel's Pentium M on the Desktop - A Viable Alternative?
by Anand Lal Shimpi on February 7, 2005 4:00 PM EST- Posted in
- CPUs
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:
- Desktop Pentium M motherboards must use mobile chipsets, which are $10 more expensive on average than their desktop equivalents, leading to more expensive motherboards.
- 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.
- 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).
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bobsmith1492 - Monday, February 7, 2005 - link
Granted the T8000 here is an Intel fanboy, but please notice Anand was comparing clock-for-clock.T8000 - Monday, February 7, 2005 - link
There is one big difference between this review and the reviews where the Pentium M did very well: CLOCKSPEED!While others where able to get over 2.8 Ghz with aircooling, Anand got just 2.4 Ghz. This may be a coincidence, but it is the difference between surprisingly good performance and a few % below others.
As most of the benchmarks where based on the stock 2 Ghz, the difference became even greater.
So this review just shows that the stock speed Pentium M performs about 30% less with about 30% less clockspeed than overclocked versions.
A slightly redesigned version with higher voltages is not extremely unlikely to hit at least 3 Ghz. Combining that with a desktop chipset will result in stellar performance, as the benchmark scores in this review (x1.5) indicate.
But since there is no slightly redesigned version and Intel has no good reason to make one, the current Pentium M desktops will only appeal to overclockers and silent computing people.
Also, for some reason, Anand found the 90W TDP of the 2.4 Ghz A64 closer to the 20W of the P-M than to the 110W of the 3.8 Ghz P4.
CSMR - Monday, February 7, 2005 - link
That's a very good option Zebo, thanks for posting it.teutonicknight - Monday, February 7, 2005 - link
One suggestion: Why don't you start using a newer version of Premiere for testing? I personally don't use it, but every that I know who does says before Premiere Pro, the program sucked. I'm sure the render results would be much more realistic and accurate if you used a more up to date version of the programRegs - Monday, February 7, 2005 - link
I was wondering the same thing too Jeff. If you feed it more bandwidth, it would eliminate the pipeline stalls and maybe give it a chance to reach higher clock speeds. Right? Or is it still prohibited by the shorter pipeline to reach higher clock speeds?Longer pipeline = wasted clock cycles. But to me that sounds like the PM should actually scale a lot better with a speed boost. Why exactly does it scale badly compared to a P4? Could it be remedied in anyway with a dual channel memory bus?
ozzimark - Monday, February 7, 2005 - link
there's something wrong with the 3400+ in the spec tests. why is the 3000+ beating it consitantly?Warder45 - Monday, February 7, 2005 - link
Maybe I missed something but I don't see the reason for all the negitivity in the final words. The 2.4Ghz P-M was very close to the A64 2.4Ghz in many of the tests, 3D rendering seemed to slow it down but that looked like it. With better boards and memory the P-M might best the A64 in a clock for clock match up.I do agree the prices are way too high. I think Intel really needs to wake up and smell what they have cooking here. With more support and more aggressive priceing they could easily have a winner in the HTPC and SFF markets.
plewis00 - Monday, February 7, 2005 - link
Surely when someone builds a mainboard with the Sonoma (i915) platform using PCI-E and DDR2-533 then it will change. And I wouldn't have thought that's that far off assuming they don't charge rip-off prices for the technology. It would also be perfect for Shuttle systems where the emphasis is on quietness and coolness rather than so much on performance.Zebo - Monday, February 7, 2005 - link
CSMRSo's this one very soon..
http://www.xtremesystems.org/forums/showthread.php...
...more than excellent performance wise if Dothan is excellent...power differential hopefully for AMD will be nominal.
Sokaku - Monday, February 7, 2005 - link
While it is true that the A64 has way more bandwidth, I doubt that is the reason why it crushed the P-M in the Professional Applications. I think the real cause is to be found in the P-M's abillity to do FP divisions. The P-III had a pipelined FP unit, however div operations were extremly expensive. My guess would be that Intel haven't thrown much effort into improving on this.