The Pentium M (Dothan) Architecture

DFI is bringing the Pentium M platform to desktop PCs. Is this something you might be interested in? Does the Pentium M really have what it takes to out perform the best of the Intel 600-series and Extreme Edition processors?

For those of you new to the Penitum M architecture, I’ll attempt to give you a quick one-over of the high points and low points in the Intel mobile-based Dothan core processors. 

We have here the 2nd iteration of the Pentium M processor, code named Dothan.  The Dothan processor is based on the 90nm process technology and sports around 140 million transistors onto a 85mm^2 die.  Considering the Dothan’s oldest brother, the Prescott core, is 122 mm^2 in die size (about 50% larger) so you can see right away these cores differ greatly.

The Dothan core is based on the now acient Pentium III architecture, before the days of the Netburst bubble.  Though Intel’s desktop group had wild fantasies of reaching 10 GHz clock speeds on their new P4 architecture, the mobile division took a somewhat more conservative approach in order to keep things cooler.  Unlike the P4 Netburst 20+ stage pipeline, the P-M (Pentium M) architecture uses about half that many, much like our good friend the AMD Athlon 64 core. 

The P-M in its Dothan form uses a 64 KB L1 cache and a 2 MB L2 cache.  The 755 model that we are using in our review today runs at 2.0 GHz with a 100 MHz quad-pumped FSB and a 20x multiplier.  There are newer processors out now that feature a 133 MHz FSB and thus a faster memory bus because of it. 

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Our Penitum M 755 Processor (Dothan core)

It is important to note that the P-M processor does share a lot with the P4 processors specifications though.  Take the system bus interface; the P-M uses nearly the identical bus as the P4 architecture, making platform transitions much easier for their chipset divisions.  Also, the P-M uses a 479-pin package that is of the exact dimensions of the original P4 processor sockets.  The extra pin is really just included to prevent people from hap-hazardly trying to switch between the two processor architectures. 

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Go ahead and count ’em — 479 pins

Seeing as this was designed for a mobile platform, the P-M architecture has a lot of additions to make it perfect for mobile applications.  The Intel team designed the processor with lower leakage transistors that run at slightly slower speeds on the cache levels in order to conserve power.  Clock gating was implemented on the processor to allow the CPU to shut itself down in sections dynamically when certain portions are not being used.  This again allows the CPU to use less power than competing mobile processors.  Of course, the crowning achievement of Intel’s power savings, Enhanced Speedstep to allow the processor to downclock its FSB and multiplier dynamically to conserver even more power.

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Heatsinks for the P4 LGA775 and Athlon 64 in the back; Pentium M in the front

What do all of those optimizations add up to?  Look at the image above and you’ll see.  A processor that performs very well in the current market, able to be cooled by a heatsink that is less than one third the size of the competition’s.  Plus, it’s a heck of a lot quieter as well.

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