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Laptop PCs need longer battery life. I used a flash-disk based laptop for much of the ’90s and loved its 10-hour laptop battery life. You just have so much more freedom when you don’t need to worry about keeping a laptop battery charged.

I’ve been very interested in how flash drives could extend notebook battery life. Using a Kill-a-watt power meter I ran some experiments with an Intel Core Duo notebook. Power use is a little more complex than I’d thought. Here’s what I found.

Laptop config:

• MacBook with the 2 GHz Core Duo,
• 2 GB RAM,
• Intel 950 integrated graphics,
• 13 inch screen,
• 8x DVD Drive,
• 160 GB Western Digital Scorpio 2.5″ 5400 RPM HDD,
• Bluetooth,
• Wi-FI

One of the nicest things about the MacBook is that disk drive removal is easy (see the 1 minute video here). I ran the tests with the internal Scorpio drive removed and ran the MacBook off an externally powered FireWire drive.

Instrumentation
In addition to the Kill-a-watt power meter, which sits between the wall power and the MacBook’s power adapter, I also used the most excellent open source MenuMeters utility. MM shows CPU, memory, disk and network usage, typically sampled over a user-selectable 1-2 second period…

The Tests
I booted the system while video taping power usage with both the internal and external disks. I also ran a disk defragmentation tool, the estimable iDefrag to create heavy disk I/O.

Since I had the system up, I also checked some of the other subsystems. Display power consumption was measured with the display off and at minimum and maximum brightness. Optical drive consumption was checked by watching a DVD and ripping a CD. Idle power consumption with the screen off and CPU at 3-4% was also checked. I even removed a 1 GB SO-DIMM.

The Results
The surprise is that you can’t just turn features on and off to judge power use. For example, performing I/O is a CPU involving business whether to disk or over Wi-Fi. In my defrag workload the CPU utilization ran from 80-95% on both cores, for an 8 watt hit – almost 3x of a busy disk…

Tags: laptop battery

This entry was posted on Thursday, January 12th, 2012 at 8:58 am and is filed under Article. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.