that is the interesting question. There isn't really a large discrepancy for the most part. Phoronix did a piece comparing ubuntu to windows 7, and they actually were rather close. http://www.phoronix.com/scan.php?page=article&item=windows_ubuntu_pow&num=1 that said, there are a few reasons why Natty ends up using more power than previous versions.. the biggest is the ASPI changes to the kernel. Basically, there are some devices that could lock up the boot process as earlier versions would boot up. The kernel devs changed the behavior of the linux kernel, now it does not assume it can implement ASPM, it will query the ACPI bits in the BIOS on your computer if it can. Before this, it didn't check, it would turn it on regardless. Unfortunately, as these things go, many BIOS out there SUCK. Most manufacturers do little testing (as in none) to make sure their bios works according to established standards, and usually if it works with Windows, they ship it, and don't really care afterwards. Now that the Linux kernel is being polite, (and following actual ACPI standards) many devices will not report proper information to hand off to the Kernel. So Linux will now assume it can't touch it, and ASPM is disabled on the devices. for the most part, you can override this with the pcie_aspm=force command during boot. There does seem to be some devices I have that don't enable ASPM even with that for me, mostly some usb stuff on my laptop and the Intel wireless 5100 adapter. I don't know that it makes a huge difference, with the Maverick kernel, I can see idle power usage down to 18 watts, but that is all PM options enabled, and nothing running but Unity (by the way, unity is much more power efficient than the older Gnome 2.x - Who would have thought..) with the latest upstream sources from git.kernel.org or the Oneiric sources I can see it idle at about 19-20 watts. Not a lot lost. the other thing to realize is there were many scheduler changes that have been made since 2.6.38 in Natty. Many of them improve things for power utilization. One developer found that there was a problem with counters rolling over that would cause timing issues with load balancing between multiple cores, and it would wake the CPUs early, preventing them from idling in low power states. This is fixed in the upstream sources, and helps a bit with the overall performance. Maybe it is just me, but when I am actually doing something on the laptop, it doesn't seem to run the battery down as bad with the patch in, so maybe that is something. Your experience may vary, some didn't report any issues in this thread at all with natty, some even said they got BETTER life out of the battery on Natty vs others. I think it depends more on how seriously your laptop manufacturer takes BIOS debugging, as many don't try very hard. If you happen to be a lucky person with a good BIOS, like maybe a decent lenovo or something, then you might not see any issues at all. Matthew Garrett was the subject of a recent article on LWN.net that gives a good history on this. Maybe it will help more than my rambling. http://lwn.net/Articles/449448/ Most of the stuff I have read from the Devs make it look like the long term fix is going to be changes in the drivers to override the broken crap even if the BIOS is stupid. But that will take updates to the affected drivers by those who know how, and when it is appropriate to force the override on all users' hardware. Matthew Garett actually mentions this, that perhaps some things work in windows as some drivers already force the handoff of ASPM functions when windows initializes. On Mon, Jul 18, 2011 at 4:19 AM, Nicolas Michel