Single-user

• Only one user active at any given time
• Each user has their own ‘home’ directory to store their files
• OS manages permissions controlling which user can access which directories
• Example: Windows

Multi-user

• Allows many users to access the resources of the system simultaneously
• Often accessed remotely
• Processing occurs on the remote system and note on the device being used
• Uses time-sharing to distribute its resources between the users

Multi-tasking

• Method of organising computer use that allows several tasks or applications to be available at the same time
• CPU time is shared between processors by the OS’s system scheduler program
• Whilst a computer can appear to the user to be running a game and playing music at the same time, a single processor can only process one thing at any given time

Multi-programming

• Keeps multiple tasks in the memory simultaneously so that a task waiting on an I/O operation means that another task can be worked on by the CPU
• The time that the CPU spends idling is reduced and the efficiency of the system is increased

Batch

• Does not interact with the computer directly