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The Pentium M represents a radical departure for Intel, as it is not a low-power version of the desktop-oriented Pentium 4, but instead a heavily modified version of the Pentium III design (itself a modified form of the Pentium Pro). It is optimised for power efficiency, a vital characteristic for extending notebook computer battery life. Running with very low average power consumption and much less heat output than desktop processors, the Pentium M runs at a lower clock speed than the contemporary Pentium 4 desktop processor series, but with similar performance (e.g. a 1.6 GHz Pentium M can typically attain or exceed the performance of a 2.4 GHz Northwood Pentium 4 (400 MHz FSB, no HT)).
Essentially, the Pentium M couples the execution core of the Pentium III with a Pentium 4 compatible bus interface, an improved instruction decoding/issuing front end, and twice as much cache: 64k primary (as compared to the PIII's 32k, the P4's 8k or the Athlon's 128k) and 1MB secondary (as compared with the 256k or 512k in the PIII, P4 and Athlon). The usually power-hungry secondary cache uses an innovative access method to avoid switching on any parts of it not actually being accessed. Other power saving methods include dynamically variable clock frequency and core voltage, allowing the Pentium M to run slowly (typically 600 MHz) when the system is idle in order to conserve energy.
The processor forms part of the Intel Centrino platform.
Intel launched its improved Pentium M, formerly known as "Dothan," on May 10, 2004. "Dothan" Pentium M processors are the first Intel processors to be identified using a "processor number" rather than a clockspeed rating, and are known as Pentium M 735, 745, and 755 (running at 1.70, 1.80, and 2.00 GHz respectively). These 700 series Pentium M processors retain the same basic design as the original Pentium M, but are manufactured on a 90nm process. Die size, at 84 mm2, remains in the same neighborhood as the original Pentium M although the 700 series contains ~140 million transistors, most of which make up the massive 2MB cache. TDP is also down to 21 Watts (from 24.5 Watts in Banias), but dissipation at lower clockspeeds has increased. However, tests conducted by third party hardware review sites show that Banias and Dothan equipped notebooks have roughly equivalent battery life.
Revisions of the Dothan core slated for a Q1 2005 release will support a 533 MHz front side bus and NX bit.
The next incarnation of the Pentium M, codenamed Yonah, taped out in mid-September 2004 and is due to ship in late 2005. Intel has released few details about Yonah, saying only that Yonah is a dual core design targeted for manufacturing on a 65nm process.
Various news sources have speculated that Yonah implements twin Dothan cores connected by an arbiter bus. The processor is also said to have the capability to disable a core when the system does not require extra processing power.
Intel expects to launch the Merom core in late 2006. Merom will support the x86-64 instruction set, and Intel plans to use the Merom core as a basis for a new desktop core, Conroe.
| List of Intel microprocessors |
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4004 |
4040 |
8008 |
8080 |
8085 |
8086 |
8088 |
iAPX 432 | 80186 | 80188 | 80286 | 80386 | 80486 | Pentium | Pentium Pro | Pentium II | Celeron | Pentium III | Pentium 4 | Pentium M | Itanium | Itanium 2(note: italics indicates non-main branch µPs) |
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