Boosting the tech-heavy Nasdaq .IXIC and the S&P 500 .SPX was Microsoft CorpMSFT.O. By Carolina Mandl and Johann M Cherian Feb 7 (Reuters) - U.S. stocks gained in choppy trading on Tuesday as investors digested comments from Federal Reserve Chair Jerome Powell about how long the fight to tame inflation may take. "We didn't expect it to be this strong," Powell said at the Economic Club of Washington, referring to last Friday's nonfarm payrolls report for January, but it "shows why we think this will be a process that takes quite a bit of time."