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 http://www.xpnet.com/). 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...