Source -Microsoft is producing a steady stream of interim Windows 7 Service Pack 1 Builds on the way to the first beta development milestone, but so far has yet to make public any official details on the first major upgrade to the latest iteration of its Windows client. Information from a third-party source reveals that, between January 11 and March 2, Microsoft compiled no less than 35 builds of Windows 7 SP1, at the rate of almost one per day. According to Russian website Wzor, Windows 7 SP1 continues to be in pre-Beta stage, and will not graduate to fully fledged Beta for another month and a half.
Windows 7 Service Pack 1(SP1) Beta in Mid-April 2010 - Build 7601.16518.100302-1530 is the latest assembly - Softpedia