Many operating systems, including UNIX, OS/2, and Windows, are capable of running many tasks at the same time and are called multitasking operating systems.

In most operating systems, there is a one-to-one relationship between the task and the program, but some operating systems allow a program to be divided into multiple tasks. Such systems are called multithreading operating systems.

The terms task and process are often used interchangeably, although some operating systems make a distinction between the two.