Mobile Pentium 4 Is Now Here
It took Intel a mere 15 months until Pentium 4 was finally fit for mobile devices. The first Pentium 4 core, going by the code name of 'Willamette,' was unable to meet the power and thermal requirements of a mobile environment. The 0.18 micron Willamette core was big, power hungry and hot. The door into the mobile world was finally pushed open for Pentium 4 when Intel had finished the 0.13 micron 'Northwood' core, as found in all desktop Pentium 4 models with the 'A' at the end. Northwood is much smaller, needs a lot less power and doesn't get nearly as hot as its older brother Willamette. In the interim, the Pentium IIIm 'Tualatin' at 1 - 1.2 GHz filled the void. In fact, many of the strides made in the Pentium IIIm are evident in the design of the Pentium 4m.
From a processor architecture point of view, Pentium 4m is identical to the new desktop Pentium 4 A processors. It comes with the same features and the same 512 Kbytes of second level cache. However, due to its nature as a mobile processor, Pentium 4m comes with a boatload of power-saving features that cannot be found on desktop Pentium 4 CPUs. You'll also find that Pentium 4m has, with its 479 pins, one pin more than its desktop brother. The power-saving features of Pentium 4m are already known from the latest Pentium IIIm processors. A 'Deeper Sleep Alert State' allows the CPU to run with very little power, while still able to 'wake up' extremely quickly. The 'Enhanced SpeedStep' technology allows throttling according to software performance requirements, rather than just according to the power source.
The Pentium 4m and the Pentium IIIm are both built on a 0.13 micron process technology. The Pentium 4m features an average power rating of less than 2 W when running in 'Battery Mode' at 1.2 V, throttled down to 1.2 GHz. Pentium IIIm required an average power rating of 1.5 watts in the same mode when running throttled down to 800 MHz at 1.15 V. At full speed, Pentium 4m requires 1.3 V, while Pentium IIIm requires 1.4 V for full speed operation. As nice as those 1.5 or 2 W of average power rating in battery mode may sound, little should we forget that those mobile processors burn a lot more power in full speed mode, either when the notebook is connected to an AC-power source or in case the user manually switched to full speed mode in battery operation. In this case, Pentium 4m has a 'TDP' (Thermal Design Power) of 30 W, and Pentium 3m at 1.2 GHz is specified with a TDP of 22 W. The TDP is the amount of thermal power that needs to be removed in a real world software worst-case scenario. The notebook designers have to ensure that their new Pentium 4 notebooks have a thermal design that allows the removal of up to 30 W of heat.
Of course, Intel also introduced a new chipset for Pentium 4m, the i845MP. As you can guess by its name, this chipset is obviously based on the i845 chipset known from desktop systems. The i845MP runs with either up to 1 GB SDRAM or DDR-SDRAM memory, and consists of the MCH-M north bridge and the already known ICH3-M south bridge that can also be found in Pentium 3 notebooks with 830 chipset.
Don't get too excited about Pentium 4m's power requirements. The major "power drainer" of today's notebooks is not the processor anymore. Especially power hungry is the display, but other components do their part, as well; for example, hard drives have a larger impact on overall power usage. Therefore, Pentium 4 notebooks should run neither significantly shorter nor longer than modern high-end Pentium III notebooks.