Intel's Pentium M on the Desktop - A Viable Alternative?by Anand Lal Shimpi on February 7, 2005 4:00 PM EST
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Low Latency L2 CacheWe 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.