Microsoft opened up registration for its 2014 Build conference yesterday, and it has sold out just over 24 hours later. This year’s event takes place in San Francisco again, but Microsoft will play host at the Moscone Center between April 2nd and 4th. After holding Build 2013 in June, Microsoft is pushing its annual event forward a couple of months this year and is expected to unveil Windows Phone 8.1 alongside some initial Windows 9 details. Microsoft will also likely detail its upcoming Update 1 release for Windows 8.1 at Build 2014.