At first, computers lacked any form of operating system. The computer user had sole use of the machine. The user would arrive at the machine armed with his or her program and data, often on punched paper tape. The program would be loaded into the machine, and then the machine set to work, until the program stopped. Later, computers came with libraries of support code which were linked to the user’s program to assist in operations such as input and output. This would become the start of the modern-day operating system.
However, these machines still only ran a single job at a time.