The first update to Windows 8.1 could launch on March 11, according to the ever-accurate Mary Jo Foley and her "trusted" sources. Windows 8.1 Update 1 could launch alongside Windows Phone 8.1 on this date, ahead of Microsoft's BUILD conference in April, where Windows 9 'Threshold' is set to be detailed.
Compared to the release of Windows 8.1 itself, Windows 8.1 Update 1 will be a minor update that shouldn't introduce many features. From several leaks showing off Update 1, we know that the update will include the ability to pin Modern UI apps to the desktop's taskbar. There will also reportedly be a close button for Metro apps coming in Update 1, making it easier for all users, especially those with mice and keyboards, to clear out apps that are running on their device.
At this stage it's unknown if Update 1 will bring the return of the Start menu, as was rumored several weeks ago. Foley says she would be "surprised" if the Start menu was included with this update; it's more likely to return in Threshold at the latest, or perhaps a second Update 2.
Microsoft's traditional 'Patch Tuesday' for March falls exactly on March 11, which is when Update 1 is expected. According to Foley, Update 1 will be delivered for free through Windows Update, as opposed to the Windows Store that was used to deliver Windows 8.1.