Michael Dell, 40. announced that he will be stepping down later this year as CEO of Round Rock-based Dell, Inc. . Kevin Rollins, Mr. Dell’s longtime partner in running Dell Inc., will take over as CEO of the computer company in mid-July while Mr. Dell will remain chairman of the board. This new arrangement is similar to the one that Microsoft Corp adopted in 2000, when Bill Gates became chairman and chief software architect and Steve Ballmer took over as CEO. Mr. Dell founded Dell in May 1984 when he was a 19-year-old just finishing his freshman year at the University of Texas at Austin. When the company went public four years later, Mr. Dell kept the titles of chairman and CEO.