[citation][nom]Kamab[/nom]The most power consuming item in a tablet is the LCD. Even if the processor was twice as efficient that wouldn't translate to 2x battery life.[/citation]
A few resons make this possible:
1) not having a retna display means a lot less pixles, which means a much less power hungry GPU, and much less power hungry display. I'll be the first to say that retna is pretty damn amazing, but for everyday use I do not really feel a huge difference between it and a normal high res display.
2)Intel's approach of having massive amounts of high power use to chew through a work load, and then go to a near 0W idle is extremely effective for mobile applications, and the A5 chips simply do not work that way. It would not be so good in a high CPU useage enviornment like heavy gaming, or video editing, but you simply do not see those types of loads on a tablet, so it is not an issue.
3) Win8 is extremely lightweight. The OS size is ~1/2 of win7 on disc alone. Removing the effects of the Aero interface makes the interface extremely efficient from a processing standpoint. Syncing when applicaitons access the internet for updates means much more down time for components like your CPU and wireless. Even in my netbook I was a near 1/3 increase in battery life (~4hrs to now a bit more than 5 hours), so the OS has a lot to do with battery life. And lets face it... OSX and iOS are not exactly 'light weight' operating systems anymore. As proved on this website, win7 (installed on a mac) runs measurably faster than OSX, and win8 will take that further, and faster means things get done quicker, and hardware can idle sooner.
4) Lastly we need to look at the simple difference between ARM and x86. ARM can be built smaller (much smaller), and thus use less wattage (much less wattage) when under load, but if it takes longer to do the same task then it is not only the wattage of the CPU that drains the battery, but also the wattage of the GPU, wireless, northbridge, ram, etc. By shutting down sooner it saves power on the overall platform, not just the CPU.
Will it 'kill the iPad'? Not likely. But it will expand the market to people like myself who are not exactly big apple users. Maybe expand the market enough to take the crown... but to kill the ipad you need something more potent than this. I use apple products on a regular basis, but Windows is what I am use to working with, and quite frankly it is (at least at the moment) the better OS. But the iPad has so many other incentives for schools, and such a good app base in place for many work places, which are 2 huge areas that win8 is missing, and will have a hard time catching up in to really kill apple off even if they do take the bulk of the single user market.