In the beginning, computers were very expensive. Only big companies could afford them. That was the breeding ground for Service Bureaus. The Service Bureau owned a computer and a software package, typically a financial one. It then offered financial services, based on computer time sharing and terminal access. This made up a centralized computer solution for e.g. accounting available at affordable prices, because many companies could share the total cost. Service Bureaus were common in the 70s, before the PC and the Macintosh changed the rules. Or rather, created a temporary break of two decades in the trend of hiring IT services.