Note: Build 2013 Day 2 will begins on Thursday, June 27 and Day 3 on Friday, June 28, with a live stream available hereYou can still watch Day 1, including a keynote address from Microsoft CEO Steve Ballmer by clicking here.

A live stream is available as Microsoft (NASDAQ: MSFT) hosts a developers' conference, Microsoft Build 2013, to introduce Windows 8.1. Also called Windows Blue, the update to the Windows 8 operating system will reintroduce the Start button as well as a boot-to-desktop option.

Click here to see a live stream of the event. A preview version of Windows 8.1 is available for the desktop, and that beta (recommended by Microsoft for "experienced PC users only") is available for download here. Windows 8.1 is a free update to Microsoft's Windows 8 and has also been called Windows Blue.

Windows 8.1, introduced at Microsoft Build 2013 in San Francisco, does not yet have an offical release date. Microsoft has said Windows 8.1 will roll out to consumers "later this year."

CEO Steve Ballmer gave the keynote speech where he said that Build 2013 was "about the transformation that we are going through as a company to move to an absolutely rapid release cycle." Ballmer said that a rapid release cycle for Windows products would be the "norm" that developers could "expect" from Microsoft from now on.

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