Thursday, May 17, 2007

The Vista Aero vs. Battery Life Myth

Lately, there has been a rash of unscientific reporting around the issue of Windows Vista and notebook battery consumption. Some customers have apparently reported decreased battery life under Vista, however, most of these reports have been entirely anecdotal in nature: Someone quoting someone else who claims that some notebook has somehow lost some of its battery life under some version of Vista (wow, that's a lot of...err..."something").

Many pundits have pointed to Vista's Aero Glass UI as the source of the power-drain. They assume (wrongly, as it turns out) that rendering the UI via a dedicated graphics processing chip - instead of using the primary CPU to draw a series of bitmaps images - somehow consumes more battery power. Since my own experiences with Vista (six months as my full-time OS on three different notebooks, with Aero enabled on all of them) seem to contradict these reports, I decided to do some objective benchmarking to set the record straight.

To ensure a representative test bed I selected two systems from different vendors operating at opposite ends of the notebook power/performance spectrum:

1. A Dell XPS M1710 with 2GHz Core 2 Duo (T7200) CPU, nVidia GeForce 7900GS graphics, 2GB of DDR-2 (667MHz) RAM and an 80GB, 7200RPM hard disk. This is hardly a "power-miser" rig. In fact, the various components - in particular, the 7900GS card - are notoriously power-hungry, at least during 3D graphics/gaming tasks.

2. A Lenovo ThinkPad R60e with 1.66GHz Core 2 Duo (T5500) CPU, integrated Intel 945 series graphics, 2GB of DDR-2 (533MHz) RAM and a 60GB, 5400 RPM hard disk. This is more of a mainstream system for business class users. It lacks the power-hungry discrete graphics, oversized LCD screen, etc.

The test consisted of multiple iterations (10x) of the OfficeBench test script (part of the DMS Clarity Suite toolset - see I configured both systems to use Vista's Power saver battery scheme and also configured OfficeBench to pause frequently (1-3 seconds per test section) to allow an opportunity for the CPU to throttle-down and/or power-management features to kick-in.

Starting from a fully-charged (100% as reported by Vista's battery meter) state, I pulled the plug on each system and allowed them to complete the test script. I then repeated this sequence, only this time I manually disabled desktop composition (i.e. turned-off the Aero UI) via the Compatibility tab in the Clarity Studio application shortcut. This caused Vista to stop the "dwm" service and render the entire script workload - the application windows, dialogs, animations and transitions - using the older, non-GPU-accelerated model.

As I suspected, the battery consumption for the non-Aero scenario was within 1-2% of the consumption with Aero enabled. In other words, disabling Aero had little or no measurable impact on battery consumption under Windows Vista Ultimate when running a mix of common business productivity (Internet Explorer, Word, Excel and PowerPoint) applications.

So much for that myth...