The Computer History Museum has come a long way since its start in a closet at the Digital Equipment Corporation in 1975, as is evidenced by the institution’s $19 million renovated facility opening its doors to the public Thursday. The renovated museum, housed in the former headquarters of Silicon Graphics and purchased for $25 million in 2002, has added 25,000 square feet of exhibition space and another 5,000 square feet for a lobby that includes an orientation theater, museum store and cafe.