Basic Operating System(BOS) An early [when?] {IBM} {operating system}. According to folklore, BOS was the predecessor to {TOS} on the {IBM 360} and it was {IPL}'d from a {card reader}. It may have been intended for very small 360's with no disks and limited tape drives. BOS died out really early [when?] as disks such as the 2311 and 2314 became common with the {IBM 360}, whereas disks had been a real luxury on the {IBM 7090}. (1999-01-29)