Feature I - Multitasking

The Amiga implementation

The Amiga implements multitasking through the operating system's kernel, Exec. It is Exec's job to handle multitasking. Exec uses a state-mechanism, each task can have one of three main states: Waiting,Ready and Running.

A waiting task is a task which is busy waiting for the result of an action, such as the user pressing a button on screen, the disk to finish loading or similar things.

A ready task is a task which is not waiting for anything, but which is not currently running. It is waiting for Exec to give it it's 'turn'.

The running task is the task that is currently executing. It will remain running for a specified time, until it needs to wait, or until a process with a higher priority becomes 'ready'.

Task's and Processes

Under Amiga OS, there are two building blocks for multitasking, the first is a task, the second is a process.

A task is the basic building block used by Exec to run the multitasking system. A process on the other hand, is created by the Amiga-Dos library. The differences are minor, but important. The main difference between tasks and processes is that a task is not allowed to call any Amiga-Dos functions. Which means a task cannot use files and file-handles and can't, as a result, print output to the screen using standard IO functions.

Please click here to continue.