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
Low Latency L2 Cache
We mentioned at the start of this review that the Pentium M featured a very large, yet low latency L2 cache - at 2MB for the current 90nm Dothan based Pentium M. But how much low latency are we talking? To find out, we turned to ScienceMark 2.0 and Cachemem.First, let's have a look at the latency of the Pentium M's 64KB L1 cache:
| Cachemem L1 Latency | ScienceMark L1 Latency | |
| AMD Athlon 64 | 3 cycles | 3 cycles |
| Intel Pentium 4 (Northwood) | 1 cycle | 2 cycles |
| Intel Pentium 4E (Prescott) | 4 cycles | 4 cycles |
| Intel Pentium M | 3 cycles | 3 cycles |
With such a large L1 cache, it is difficult to get much lower than 3 cycles, as we see that the Pentium M has a similar L1 access latency as the Athlon 64. What is also important to note, however, is that the Pentium M does have a lower L1 access latency than the Pentium 4E.
But what we came here to look at was L2 cache latency, which matters much more in real world application performance where not everything fits into L1:
| Cachemem L2 Latency | ScienceMark L2 Latency | |
| AMD Athlon 64 | 17 cycles | 18 cycles |
| Intel Pentium 4 (Northwood) | 16 cycles | 16 cycles |
| Intel Pentium 4E (Prescott) | 23 cycles | 23 cycles |
| Intel Pentium M | 10 cycles | 10 cycles |
Here's where things get very interesting - the Pentium M has the lowest L2 cache access time of any of the modern day desktop microprocessors. With a 10 cycle L2 latency, any application that fits within the Pentium M's 2MB cache will most definitely perform very well on the CPU. It is the 10 cycle L2 that allows the Pentium M to be competitive with much higher clocked CPUs in most mobile applications as they are normally office application tasks that are generally very cache-friendly. Keep this in mind as we look at the actual performance numbers of the Pentium M.
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Jeff7181 - Monday, February 7, 2005 - link
Give the Dothan a speed bump and some dual channel DDR400 and stay out of it's way...MDme - Monday, February 7, 2005 - link
well, now we FINALLY have a comprehensive review of the P-M, it's strengths and weaknesses. While the P-M is good. the A64 is still better.Netopia - Monday, February 7, 2005 - link
Yeah, I was about to say the same as #3.Why did you go to the trouble to list what the AthlonXP system would have in it and then not actually test or reference it anywhere in the article?
I still have a bunch of AXP machines and regularly help others upgrade using XP-M's, so it would be interesting to see these at least included in reviews for a while.
CrystalBay - Monday, February 7, 2005 - link
Hi, I noticed in the testbed an AXP3200/NF2U400 but there are no charts with this setup.Beenthere - Monday, February 7, 2005 - link
It's a pipe dream for those who wish Intel had their act together. It's already confirmed M don't scale well and is not effective for HD computing. It's performance is really some place between Sempron and A64 but certainly not a suitable competitor to A64 nor FX. Just another Hail Mary for a defunct Intel.coldpower27 - Monday, February 7, 2005 - link
Hmm, an interesting review on the Pentium M to say the least. Though are 2-2-2-10 timings for the Pentium M the best for this architecture???0ldman79 - Wednesday, January 26, 2022 - link
It's interesting coming back and reading this after it's all settled, Core 2 seemed to be an evolution of the Pentium M line.Intel did hang the Netburst architecture up, though they added a lot of Netburst's integer design to Core 2 while designing Nehalem. AMD apparently believed that Intel was going to stick with Netburst and designed the FX line, while Intel went back to their earlier designs and lowered the clock speed, massively increased the IPC and parallelism and out-Phenom'ed the Phenom with Nehalem.
Back then Intel believed that Dennard scaling would continue and they'd have 10GHz chips, turns out wider and slower is better.