The Third Generation of Operating Systems brings us back to the period 1965-1980. Its main key to success is multi-programming
In the early 1960s, the computer industry had two completely different product lines. The first line was used for numerical calculation purposes in science and engineering. The second line was that of commercial computers used for orders and for printing invoices, in banks and insurance companies. Holding these two lines was very costly for companies, and moreover, it was crystal clear the trend was to launch other new lines.