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Intels Centrino(TM) technology consists of three parts: a Pentium M processor, a chipset, and a wireless module. Let's see how these parts are supported under Linux so far. For an official statement from Intel about Linux support, see their OS compatibility survey.
Here you may find current information about Linux on Centrino laptops and notebooks.
According to Intel's OS compatibility survey , the Pentium M processor family is supported. Robert Freund has written a concise HOWTO about controlling ACPI Centrino(TM) features via software in Linux. He describes how to control CPU frequency and other energy saving modes, as well as how to get information about the battery state.
The Intel 855/915 chipset families are designed to deliver better performance at lower power. The chipsets are available as discrete memory controller hub (e.g. Intel 855PM). Or as an integrated graphics and memory controller hub (e.g. Intel 855GM). Intel provides the Extreme Graphics driver for Linux, which includes AGP GART and DRM kernel modules as a binary files. I have no experience with this drivers, because the chipsets work with XFree86/X.org drivers, too. The Pentium-M CPU may come accompanied with other graphics chipsets too, e.g. from ATI, nVIDIA or Trident.
There are different solutions to get these cards running with Linux: drivers from Intel, NDIS wrapper and Linuxant driverloader (commercial).
ipw2100, Intel's Open Source driver with included firmware, for the first Centrino generation (incl. WEP and WPA together with HostAP). For the second generation of Intel's miniPCI modules: PRO/Wireless 2200BG (802.11g/802.11i), the ipw2200 project provides a driver. Third generation PRO/Wireless 2915ABG (IEEE 802.11b, 802.11g und 802.11a) miniPCI cards will be supported by the ipw2200 project, too.
Intel didn't provide drivers, when the begun to sell their Centrino technology. During this time there have been other solutions: Some vendors refuse to release technical specifications or even a binary Linux driver for their WLAN cards. NDIS wrapper tries to solve this by making a kernel module that can load NDIS (Microsoft-Windows Network Driver Interface Specification) drivers. Currently there are two implementations available. The commercial Linuxant Driverloader supports a broad range of chipsets including Intel's PRO/Wireless 2100 LAN Mini-PCI Adapter. There is also ndiswrapper an Open Source solution by Pontus Fuchs.
As another workaround was the usage of a Linux-supported miniPCI WLAN card. These cards are difficult to get, but some desktop WLAN PCI cards contain miniPCI cards. Often it is a tedious task to build them into a laptop. Kernel maintainer Theodore Tytso has written a manual about achieving this task. You may also use a wireless PCMCIA or CF card instead. This solution may provide more flexibility, because you may use a PCMCIA or CF card in different devices and choose the Linux driver of your choice. You may also extend the wireless range by adding antennas to some cards. For Linux compatibility there is the TuxMobil PCMCIA/CF Card Survey. In the future, manufacturers will probably offer alternative miniPCI solutions. DELL is already doing so for their Latitude D series.
Though Linux support is not yet complete, some features of the Centrino(TM) technology already make it worthwhile to take into account when buying your next laptop. Though the new CPUs are named so similarly to existing ones that some people mix them up, they are completely different inside. Compared to the Pentium-4 Mobile CPU, the Pentium-M will allow a smaller form factor for laptops, making them more portable and lighter. Because of their higher clockspeed, the Pentium-4 CPUs have produced too much heat to build them into slimline notebook cases. Therefore, very flat notebooks have only been available from Apple or with a Pentium III Mobile CPU. Also, the battery power the Pentium-M consumes for a given level of performance will decrease, but I do not have a benchmark about how much the savings actually are yet. PENN Computing offers a nice comparison of Pentium-M and Pentium-4 Mobile. Note: The character M in Pentium-M suggests "mobile". Therefore some people mix this kind of CPU with the mobile versions of the Pentium-III/Pentium-4 CPU.
Laptops based on the Centrino(TM) features are already very popular in the Linux community. Installation reports for almost all Centrino based laptops available at TuxMobil.