Memory management

Multi-tasking OS - A multi-tasking operating system allows more than one program to run at the same time - or at least they appear to run concurrently. eg Windows, OS X, Linux and Android

Multi-user OS - There is a single computer (the mainframe) with the OS, then multiple terminals/workstations, that are not running their own operating systems,

Distributed OS - A group of computers called a 'cluster', work together to undertake a single computer-intensive task. Each computer contains part of the overall operating system.

Real Time OS - It is extremely reliable and has very precise and consistent timings. If two inputs arrive at the same time, the RTOS programmer is able to set a priority to them. eg factory production, car management

Embedded OS - An embedded system is a microprocessor designed to perform a dedicated function, as a part of a larger piece of equipment. These devices need an embedded OS to run.

Batch OS - A mainframe computer that is designed for huge repetitive data processing, eg doing the same task over and over again. For example, a mainframe set up to process 30 million pension statements, each one calculated for a specific customer.