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
Memory Latency and Bandwidth
Currently, there are only two manufacturers of desktop Pentium M motherboards who are selling into the channel - AOpen and DFI. Both AOpen and DFI's motherboards came about not because of widespread consumer demand, but because they each had one customer that needed a Pentium M motherboard for a specific application. Once the boards were designed and built, they were later repackaged and made available to the public as an afterthought.The major issue with both of these motherboards is that they are based on the 855GME chipset. The 855GME only features AGP 4X support, but the killer is in its single-channel DDR333 memory controller. Without DDR400 support, the 855GME starves the Pentium M for bandwidth, as it is only capable of delivering 2.7GB/s of bandwidth to main memory while the Pentium M at 2.0GHz needs 3.2GB/s of bandwidth to remain most efficient. Overclocking the memory bus is somewhat of an option, but not exactly the most desirable one for reasons that we will get to later.
One solution is Intel's recently released mobile 915 chipset, which features a dual-channel DDR1/DDR2 memory controller. The dual channel controller is more than capable of supplying the appropriate memory bandwidth to the Pentium M, if not a bit overboard, but right now mobile 915 isn't an option on the desktop.
With an unsatisfactory amount of memory bandwidth, the Pentium M will undoubtedly be held back in performance in applications where memory bandwidth is most important. As we all know, memory bandwidth and latency are interdependent, so let's see how the latency to main memory compares.
For our memory latency tests, we once again turn to ScienceMark 2.0:
| CPU | Memory Latency (in ns) |
| AMD Athlon 64 3200+ (2.0GHz) | 50ns |
| Intel Pentium 4E 560 (3.6GHz) | 80ns |
| Intel Pentium M 755 (2.0GHz) | 80ns |
With an on-die memory controller, the Athlon 64 obviously offers the lowest latency memory access out of the group. The reason why we used a 2.0GHz Athlon 64 for this comparison was to show the memory latency seen by a CPU clocked identically to the Pentium M. As strong as the Pentium M's branch predictor may be, the trip to main memory will always be longer than the Athlon 64 - increasing the penalty from having a longer pipeline.
When you compare the Pentium M to the Pentium 4, you see the real harm in only having a single channel DDR333 memory controller - the time for the Pentium M to get to main memory is very similar to that of the Pentium 4, even when the latter is using higher latency DDR2 memory. High memory latency will send the performance of the Pentium M tumbling as soon as it leaves the sanctity of its 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 :PZebo - Monday, February 7, 2005 - link
I myself have been guilty of hyping dothan after seeing GAMEPCs "opimistic" review. This should quell that.:DZebo - 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
testKalessian - 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)