Update begins rolling out to users at 4 a.m. Pacific Time.

Windows 8.1 Blue Windows 8.1 launches today

Windows 8.1 is rolling out today via the Windows Store. Microsoft is releasing the refresh to Windows 8 at 4 a.m Pacific Time, which puts it in the hands of North American users early Thursday morning, European users during the early afternoon and in the evening for users in Asia.

Windows 8.1 contains a variety of features and improvements, such as deeper integration with Microsoft’s web products like Skydrive and Bing, as well as a new split-screen mode that promises to improve multitasking.

The biggest change in the new operating system is the re-inclusion of the start button, and the de-emphasis of the user interface formerly known as Metro. Users now have the option to boot directly to the desktop, bypassing the touch-centric user interface entirely.

For Microsoft, this represents an admission that the UI was a failure. While it might have its place in touch environments such as tablets or smartphones, PC users rejected it enthusiastically.

But Microsoft’s Windows 8 problems aren’t just limited to the the UI. As Windows XP nears its “end of life” date of April 2014, many enterprise customers aren’t upgrading. Those that do are picking Windows 7, not finding a definite reason to make the jump to Microsoft’s new OS.