Pentium M

Lore & Background

The Pentium M evolved from the core of the last Pentium III–branded CPU by adding the front-side bus (FSB) interface of the Pentium 4, an improved instruction decoding and issuing front end, improved branch prediction, SSE2 support, and a much larger cache. The first Pentium M–branded CPU, code-named Banias, was manufactured on a 130 nm process, released at frequencies from 900 MHz to 1.7 GHz using a 400 MT/s FSB, and had 1 MB of L2 cache. The Banias family internally supports Physical Address Extension (PAE) but does not show the PAE support flag in its CPUID information, causing some operating systems to refuse to boot. The Dothan core, launched on May 10, 2004, was manufactured on a 90 nm process with 2 MB L2 cache and initially used a 400 MT/s FSB; later revisions in the first quarter of 2005 supported a 533 MT/s FSB and enabled the PAE support flag. Dothan models were identified by processor numbers rather than clock speeds, and included low-voltage and ultra-low-voltage variants with TDPs as low as 5 W.

Reader's Guide

The Pentium M was notable for its power efficiency, running at lower clock speeds than the Pentium 4-Mobile but with similar or better performance—a 1.6 GHz Pentium M could typically match or surpass a 2.4 GHz Pentium 4-M. It used SpeedStep 3 technology to dynamically vary clock frequency and core voltage, throttling to intermediate clock states (e.g., 600 MHz, 800 MHz, 1000 MHz, 1200 MHz, 1400 MHz, 1600 MHz) to conserve energy. The large L2 cache used an access method that only switched on the portion being accessed, reducing power consumption. Although marketed exclusively as a mobile product, motherboard manufacturers such as AOpen, DFI, and MSI shipped Pentium M compatible boards for non-mobile enthusiasts, HTPC, workstation, and server applications. The Pentium M line was removed from official price lists in July 2009, succeeded by the mobile Pentium Dual-Core line. Its legacy includes influencing the design of the Intel Core brand processors (Core Duo and Core Solo), which were based on the Enhanced Pentium M architecture.

Did You Know?

• The Pentium M was designed by Intel's Haifa team, which had previously worked on the memory controller for Timna.
• A 1.6 GHz Pentium M can throttle to clock speeds of 600 MHz, 800 MHz, 1000 MHz, 1200 MHz, 1400 MHz, and 1600 MHz using SpeedStep 3.
• The Pentium M 740 has been tested to perform up to approximately 7,400 MIPS and 3.9 GFLOPS (using SSE2).
• The Banias core does not show the PAE support flag in its CPUID, causing boot failures in some Linux distributions and Windows 8 and later.