The original Macintosh system software was partially based on the Lisa OS, previously released by Apple for the Lisa computer in 1983. As part of an agreement allowing Xerox to buy shares in Apple at a favorable price, it also used concepts from the Xerox PARC Xerox Alto, which Steve Jobs and several other Macintosh team members had previewed. Mac OS has been preinstalled on every Macintosh computer made, and has been sold separately in retail stores until being distributed exclusively online.