Gecko's CPU Library

Intel Pentium M (Banias) processors

Introduction: March 2003


The Pentium M brand refered to only two single-core 32-bit x86 microprocessors (with the Intel P6 microarchitecture) introduced in March 2003 (during the heyday of the Pentium 4 desktop CPUs), and forming a part of the Intel Centrino platform. The Pentium M branded processors had a maximum power consumption (TDP) of 3-25W, and were intended for use in laptop personal computers (thus the "M" moniker standing for mobile). They evolved from the core of the last Pentium III branded CPU by adding the bus interface of Pentium 4 one, an improved instruction decoding/issuing front end, improved branch prediction, SSE2 support, and a much larger cache. The first Pentium M branded CPU, codenamed the Banias, was followed by the second one - the Dothan. After the Pentium M branded processors, Intel released the Core branded dual-core mobile Yonah CPU with a modified microarchitecture. Pentium M branded CPUs can be considered as the end of the Intel P6 microarchitecture.

The Pentium M represented a new and radical departure for Intel, as it was not a low-power version of the desktop-oriented Pentium 4, but instead a heavily modified version of the Pentium III Tualatin design (itself based on the Pentium Pro core design). It was optimised for power efficiency, a vital characteristic for extending notebook computer battery life. Running with very low average power consumption and much lower heat output than desktop processors, the Pentium M ran at a lower clock speed than the laptop version of the Pentium 4 (the Pentium 4-Mobile, or P4-M), but with similar performance - a 1.6GHz Pentium M was typically able to attain the performance of a 2.4GHz Pentium 4-M. The Pentium M (model 740) had been tested to perform up to about 7,400MIPS and 3.9GFLOPS (using SSE2).

The Pentium M coupled the execution core of the Pentium III with a Pentium 4 compatible bus interface, an improved instruction decoding/issuing front end, improved branch prediction, SSE2 support, and a much larger cache. The usually power-hungry secondary cache used an access method which switches on only the portion being accessed.

Other power saving methods included dynamically variable clock frequency and core voltage, allowing the Pentium M to throttle clock speed when the system was idle in order to conserve energy, using the SpeedStep 3 technology (which had more sleep stages than previous versions of SpeedStep). With this technology, a 1.6GHz Pentium M was effectively able to throttle to clock speeds of 600MHz, 800MHz, 1000MHz, 1200MHz, 1400MHz and 1600MHz; these intermediate clock states allowed the CPU to better throttle clock speed to suit conditions. The power requirements of the Pentium M varied from 5 watts when idle to 27 watts at full load. This was useful to notebook manufacturers as it allowed them to include the Pentium M into smaller notebooks.

Although Intel had marketed the Pentium M exclusively as a mobile product, motherboard manufacturers such as AOpen, DFI and MSI had been shipping Pentium M compatible boards designed for enthusiast, HTPC, workstation and server applications. An adapter, the CT-479, had also been developed by ASUS to allow the use of Pentium M processors in selected ASUS motherboards designed for Socket 478 Pentium 4 processors. Shuttle Inc. offered packaged Pentium M desktops, marketed for low energy consumption and minimal cooling system noise. Pentium M processors were also of interest to embedded systems' manufacturers because the low power consumption of the Pentium M allowed the design of fanless and miniaturized embedded PCs.

The Banias core

As the M line was originally designed in Israel, the first Pentium M was identified by the codename Banias, named after an ancient site in the Golan Heights. Given the product code 80535, it initially had no model number suffix, but was later identified as the Pentium M 705. It was manufactured on a 130 nm process, was released at frequencies from 900MHz to 1.7GHz using a 400MT/s FSB, and had 1MB of level 2 cache. The core average TDP (Thermal Design Power) is 24.5 watts.

The CPUID signature for a Banias was 0x69X.

Source: Wikipedia, the free encyclopedia.