- noun a set of basic software that controls the running of the hardware and the management of data files, without the user having to operate it.
- noun the main program which operates a computer
- The software which runs all the software and hardware of a computer. It is the first program the computer loads when powered on, remains memory resident, and continuously controls and allocates all resources. Without it, for example, a computer can not recognize input, such as that from a keyboard, it can not process, as the operating system controls the use of the CPU, nor can it provide an output, as it manages all peripherals including the monitor. Its abbreviation is OS. Also called executive, or supervisor. When disk-based, also called disk operating system.