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Green computing: do Wi-Fi power saving adaptors work?

We put their power-saving consumption rates to the test

Many Wi-Fi adaptors claim to have power-conservation capability. We set out to test just how useful they are.

Test configuration and procedures

The basic test strategy was to copy a file consisting of roughly 1MB (1,095,680 bytes, to be precise) from a source computer to a destination computer as many times as possible, beginning with a fully charged battery and ending each test run when the notebook computer went into hibernation as a result of near exhaustion of the battery, defined in this case as 5 percent battery charge remaining.

The test was driven by a simple DOS .bat file, the logic for which was to print the time of day, copy the file from source to destination, pause for three seconds, increment and display a counter indicating the loop iteration, and then run continuously until the battery gave out. The purpose of the pause was to allow more than enough time for the notebook to go into PSM and to simulate a fairly low Wi-Fi usage duty cycle, so as to maximise the time the radio was asleep. The test script was run on the destination computer so that transactions would be initiated and recorded by the mains-powered computer.

The destination in all test cases was a Dell 4500 desktop upgraded with a PCI gigabit Ethernet adaptor and running Windows XP Pro with all current updates applied as of the date that testing began. Power conservation features on this machine were disabled for all test runs as it was operating on AC power.

We used two different source computers, both laptops: an Acer Aspire 5920 equipped with Vista Ultimate (including all updates available as of the date of the test run, but not including SP1), and featuring both Gigabit Ethernet ports and an integral Intel 4965 a/g/n wireless adaptor; and an HP Compaq nx6125 with gigabit Ethernet and a Broadcom 802.11 b/g radio.

Both machines were directly connected to each other either via a Gigabit Ethernet link (for baseline testing), and via a wireless connection (using an access point). At no time were any elements connected to any other network or the internet.

The Acer's built-in wireless adaptor was used in 802.11g mode only, with a Netgear WNR854T router (used only as an access point in this test) forced to 802.11g mode as well. The Asus internal adaptor was also used in 802.11n mode with a Linksys WRT350N router (again, as an access point). Similar 802.11g testing was performed with the HP laptop, using the Linksys AP, and also with two external 802.11n adaptors (a Linksys PC card and an SMC USB adaptor) connected to the Linksys AP. All of this provided a good variety of test cases.

NEXT PAGE: How the power saving adaptors fared in our test

  1. We put power-saving consumption rates to the test
  2. Test configuration and procedures
  3. How power-saving adaptors fared in our test
  4. Our verdict on power saving Wi-Fi adaptors

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