Power and performance

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External batteries aren't the only way to keep your laptop trucking for hours on end. The notebook you buy may help determine the amount of uptime you can expect on an airplane. How so? Even though the CPU consumes about half the laptop's total power, recent advances in processor technology have eased the burden placed on a notebook's battery. Now, thanks to Intel's Pentium M and Centrino technology, for instance, laptops can run faster and longer on the same batteries they used to use. Here's the lowdown on which processors let laptops last the longest.

Now that you know how batteries work, here's the latest in processor technology. Even though the CPU consumes about half the laptop's total power, recent advances have changed the equation. Now, top laptop performance can go hand in hand with long battery life. You just have to know your CPUs.

IBM's Pentium M-based ThinkPad X40

Intel Pentium M (part of the Centrino package)
Without a doubt, the Pentium M is the battery-life champ. With 77 million transistors, a megabyte of external cache, and the ability to streamline operations, it balances raw power with extensive battery life. Toss in an Intel-made Wi-Fi radio and an Intel chipset, and the Pentium M is part of the Centrino triad.

Running at up to 1.7GHz, Pentium M laptops run rings around the competition, with an average MobileMark 2002 score of 152 and an average battery life of 4 hours, 12 minutes. Two new Pentium M-based designs are on the scene. First, the new Intel Celeron M uses the same computational core but half as much cache as the Pentium M and starts at US$107, making it the value alternative. By spring, you can expect a new generation of Pentium Ms that are smaller and faster. Code-named Dothan, these chips should boost battery life.

Dell's Latitude D505 is powered by the Celeron M processor

Intel Celeron M
Based on the Pentium M, this new chip is an inexpensive alternative to the Pentium M. It runs at up to 1.2GHz and has 512MB of secondary data cache. With a 400MHz frontside bus, the Celeron M has the Pentium M's power-conservation software, which lets the CPU go into a deep sleep mode to cut consumption to a minimum. It's too early to tell what the chip's performance and battery potential will be.

Mobile Intel Celeron
The Mobile Celeron is based on the Pentium 4 core, is quite different from the Celeron M (despite the similar name), and uses more battery power. It runs from 650MHz to a top speed of 2.5GHz and supports frontside buses from 100MHz to 400MHz for a range of power and performance possibilities. Battery life is shorter than it is with laptops running a Pentium M.

Intel Mobile Pentium 4
Based on the desktop Pentium 4, the Mobile Pentium 4 runs a little slower but has the same 55 million transistors and 512MB of external cache. This chip is used mostly on desktop-replacement laptops, and it can go as fast as 3.2GHz and costs as little as US$190. Based on testing of dozens of laptops, the average Mobile P4 notebook has a score of 121 on the MobileMark 2002 benchmark and can run for 2 hours, 47 minutes, which is much shorter than the Pentium M life.

Dell Inspiron 9100 uses a 3.2GHz desktop Pentium 4 processor

Intel Pentium 4
This desktop-PC processor was originally found only on desktops, but it's now in some desktop-replacement laptops, as well. The Intel P4 is very fast and is less expensive than Mobile Pentium 4 and Pentium M chips, but it runs very hot and allows only poor battery life.

AMD Athlon XP-M
The Athlon XP-M uses AMD's QunatiSpeed and 3DNow technologies to speed up the most-used operations. With a top speed of 2GHz, the chips start at less than US$200. Athlon XP-M laptops average a MobileMark 2002 score of 99 and a runtime of 2 hours, 27 minutes, placing them behind Mobile Pentium 4 and Pentium M machines. A few laptops now feature AMD's 64-bit Mobile Athlon 64 processors. These laptops should be screamers, because they can chew through twice as much material in the same time compared to 32-bit Pentium and Crusoe processors. It's unclear so far how the chips affect battery life.

The Sharp Actius MM20 runs on the Efficeon chip from Transmeta

Transmeta Crusoe T-5800
By using Transmeta's code-morphing software, the Crusoe T-5800 off-loads some of the processor's toughest duties to software, which can save power. At a peak speed of 1GHz, the Crusoe T-5800 runs slower than the Athlon or Pentium chips and yields lower performance. Our averages show that the typical Crusoe laptop can run for 2 hours, 40 minutes, just behind the Mobile Pentium 4, but it lags on performance, with an average MobileMark 2002 score of 57.

Transmeta's new chip, currently popular in Asian markets and just recently released in the United States, is called the Efficeon. The first laptop to use this processor in the United States is the Sharp Actius MM20, a 2-pounder that can run on batteries for more than 3 hours.

Apple 17-inch PowerBook comes equipped with a PowerPC G4 processor

Apple PowerPC
Apple iBook buyers get the slower 800MHz, 933MHz, and 1GHz PowerPC G4 processor, while those who upgrade to the faster PowerBooks will get speeds as fast as 1.33GHz. All of the PowerPC chips include 512KB of external cache. While the 12-inch iBook can run for about 3.5 hours, the higher-performing 17-inch PowerBook can go only 2.7 hours between charges, according to CNET Labs tests.

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