The notebook you buy may help determine the amount of uptime you can expect on an air flight. How come? Even though the CPU consumes about half the notebook's total power, recent advances in processor technology have eased the burden placed on a system's battery. Now, thanks to Intel's Pentium M and Centrino technology, for instance, notebooks can run faster and longer on the same batteries they used to use. Here's the low-down on which processors let notebooks last the longest.
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 Level 2 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.
Intel's Centrino package comprises the Pentium M processor, the 855 chipset and a PRO/Wireless 2100 Network Connection Mini-PCI card.
Running at up to 1.7GHz, Pentium M notebooks run rings around the competition, with an average MobileMark 2002 score of 152 and an average battery life of 4 hours and 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. Soon, you can expect a new generation of Pentium Ms that are smaller and faster: codenamed Dothan, these chips should boost battery life.
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 Level 2 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 notebooks 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 Level 2 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 notebooks, the average Mobile Pentium 4 notebook has a score of 121 on MobileMark 2002 and can run for 2 hours and 47 minutes, which is much shorter than the average for Pentium M systems.
Intel Pentium 4
This desktop-PC processor was originally found only on desktops, but it's now in some desktop-replacement notebooks, as well. The Intel Pentium 4 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 QuantiSpeed 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 notebooks average a MobileMark 2002 score of 99 and a runtime of 2 hours and 27 minutes, placing them behind Mobile Pentium 4 and Pentium M systems.
A few notebooks, including Acer's Aspire 1500 range, now feature AMD's 64-bit Mobile Athlon 64 processors. These systems 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 these chips affect battery life.
The Acer Aspire 1500 uses AMD's 64-bit Mobile Athlon 64 processor.
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 Athlon or Pentium chips and yields lower performance. Our averages show that the typical Crusoe notebook can run for 2 hours and 40 minutes, just behind the Mobile Pentium 4; however, 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 US, is called the Efficeon. The first notebook to use this processor in the US is the Sharp Actius MM20, a sub-1kg system that can run on batteries for more than 3 hours.
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 Level 2 cache. While the 12in. iBook can run for about 3.5 hours, the higher-performing 17in. PowerBook can go only 2.7 hours between charges, according to our tests.
Dear reader,
Don't get confused by the descriptions above about the flow of electrons to and from the positive and negative electrodes.
A negative electrode is negative because it carries a surplus of negative charge. As electrons are negatively charged, this means that the negative electrode has an excess of electrons.
Similarly, the positive electrode is positive because it has a lack of electrons - and it is the tendancy of the electrons to move in such a way as to balance this out that causes electric current.
In other words, electrons will flow out of the negative electrode into the external circuit (in this case, the laptop's electonics), through this circuit and into the positive electrode.
The place to which the description refers is from the electrode into the electrolyte - the conductive paste that is between the electrodes inside the battery. Electrons move from the electrolyte onto the negative electrode, and from the positive electrode into the electrolyte.
The direction of flow (from the negative to the positive) is called electron current.
However, because our brains like to think in terms of positives, and because the early experimenters with electricity did not realise that the current was being carried by negatively charged particles, they defined current in terms of flow of positively charged particles from the positive to the negative. This is called conventional current.
A way of visualising this in electron flow is the opposing flow of "holes" into which an electron can move. As an electron moves forwards in the direction of electron current, the (effectively positively charged) hole moves backwards - in the direction of conventional current.
The effect is identical - charge is carried around a circuit through charged particles.