Mad Men, season 7, episode 4, describes the computer business in 1969 as follows. IBM would lease computers to businesses, but would do so only for short leases, and would replace them with newer models on the lease renewal. Therefore, a bunch of businesses had started in competition, who bought IBM computers and leased them for longer terms and cheaper.
Of course, Mad Men is fiction, but I wonder: (to what extent) is this true?