Thanks to a very interesting thread on EeeUser.com, I have gotten curious about overclocking (ie; run the CPU at its rated speed of 900MHz) versus the native underclocked speed (630MHz) versus a seriously underclocked speed of 360MHz - in particular the effect it'll may or may not have on the battery life.
Off course, there is no certain way to manually measure runtime - unless you're prepared to sit in front of the Eee with a stopwatch waiting for it to die. But, I remembered reading a review of a large capacity battery that held a clue - a shell script that would create a text file with the time of start, followed by 'touching' the file every so often to update the time stamp.
With the drivers, modules, GUI and script in place, it was time to set some input conditions:
- battery at 100%, running from external power
- brightness 10 notches up from absolute darkest
- no WiFi
- running Abiword with a open document
- running gxine with a looping mp3
- volume muted
Tests were run with a 5200mAh battery, which is a year old by now.
With all this set up, I would open the over-under clock applet and select the clock speed to test. Opening a terminal, I then started the script at the same time as I pulled the charger plug out of the back of my Eee.
Once the Eee has used up all the available juice, it powered down. Then it was a simple matter rebooting on external power and compare the time stamp of the text file with the time recorded in the file.
And now the results:
The reduction in time for overclocking is small seeing as you get a whooping 43% increase in CPU speed. It is worth keeping in mind that these tests isn't the most taxing on the CPU though, even if the CPU bar widget on the right side of the monitor was maxed out the whole time while running at 360MHz.
In short, it seems that underclocking isn't worth it if you're doing tasks that requires the CPU to be working all the time. I'll likely do a second test later to try for less CPU intensive tasks, like surfing.
The other interesting tidbit is that while running under 900MHz, you'll get the same runtime if you do light surfing or are listening to a looping MP3...
Also that free advise is worth what you pay for it, so take my results for what they are worth :)