We set out to learn more.
Yes, Windows is really less efficient (on the Mac)
To ascertain whether or not Windows crippled battery life, we needed to run different operating systems on identical hardware: in this case, the 2012 "Ivy Bridge"-based 13-inch MacBook Air. We used Apple's latest operating system, OSX 10.9 "Mavericks," as a baseline, and compared it to Windows 7 SP1 and Windows 8.1 using Apple's Boot Camp technology. We set hardware parameters to try and eliminate any hardware effects, preventing the system and display from sleeping, setting the display brightness to a uniform 150 cd/m2, and turning adaptive brightness off.
We then charged up the Air to full capacity and performed our standard Wi-Fi battery rundown test, accessing a series of Web sites until the notebook conked out. The only differences were the default browser (IE 10 for Windows 7, IE11 for Windows 8.1, Safari for the Mac OS). At Microsoft's request, we installed Flash on Safari to ensure that any Web pages were rendered completely.
The results were telling: the MacBook Air running Mac OS X "Mavericks" lasted just over 7 hours, two hours or about 29 percent longer than the Windows 7 PC. And, of course, the data indicates that "upgrading" to Windows 8.1 is really a downgrade in battery life.
So what's going on here? That's a much more complicated question.
Microsoft's explanation: optimized drivers
Naturally, our first call was to Microsoft, for an explanation. They were ready with one.
"What appears to be the most fair comparison is actually the least fair comparison," said Gabriel Aul, director of program management at Microsoft.
Apple's Boot Camp provides a thin layer of code between the operating system and the Mac hardware itself, along with drivers to access the Mac's hardware. Each driver is a bit of code that controls individual components, such as the Wi-Fi radio, for example, or the laptop's display. But according to Microsoft, the basic Boot Camp installation uses generic or at least un-optimized drivers.
And that can make a difference, Aul said. "Device firmware and buses optimized for particular power states can have a huge impact on battery life if you have something like a radio" that's not properly tuned, he said.
For example, a Wi-Fi radio's default driver setting may be set to maximum power, Aul said, to deliver the best throughput at maximum range. But that may also mean that the battery will drain even faster than usual. And when the PC constantly powers on the Wi-Fi radio to download Web sites, those small differences can add up.
"What we can observe makes us think that... [Windows] off-the-shelf devices are highly competitive on battery life," Aul said. "On that [Mac], [those drivers] may not be particularly tuned for Windows."
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