Apple just took traditional pricing for operating system updates, and turned it on its head.

During Apple’s special event this morning in San Francisco, the company announced that OS 10.9 “Mavericks,” its latest update to the Mac OS, will be available for a free download from the Mac App Store today, on compatible systems dating back to 2007, no matter what previous version of OS X a user is currently running.

The pricing is a shot across the bow of Microsoft, which offers its new Windows 8.1 update free to existing Windows 8 users, but charges $120 to $200 for people upgrading to Windows 8.1 from older versions, including the popular Windows 7.

Mavericks, which was previewed at Apple’s Worldwide Developer Conference in June, brings a number of performance boosts to the Mac. One of the key performance boosts in Mavericks is an extension of battery life, based only in software. According to Apple Senior Vice President of Software Engineering Craig Federighi, owners of Apple’s new MacBook Air can expect to get an hour and a half more time watching movies through iTunes, just by upgrading their operating system. Those benefits also trickle down to the rest of Apple’s ecosystem, though it’s not clear how concrete the benefits for other portables are.

The update also boasts a number of key feature improvements, including the ability to respond to notifications in the notification itself, rather than having to switch over to the app that generated the notification. So, if you get an IM from your friend in Messages that you want to respond to quickly, you don’t have to switch back to Messages to fire them a missive back.

In addition, Apple has knocked out one of Amazon’s key advantages in the e-book space with a new iBooks desktop app. While Amazon had a leg up on iBooks by offering a Kindle app for computers as well as Kindles and other mobile devices. Up until now, iBooks users have only had the ability to read downloaded books on their iDevices. The iBooks app isn’t cross-platform, though, so Amazon still has an advantage with Windows users.