Preemptive multitasking

Preemptive multitasking (or PMT for short) is a multitasking model in which the operating system takes control away from a program and gives it to another program, in order to ensure that all applications get their fair share of time. Most current operating systems use preemptive multitasking, although RISC OS does not currently use this model, instead opting for a model known as cooperative multitasking, where applications decide when to cede control to the operating system. However, there has been much discussion about the issue for many years, and there have been attempts to bring it to RISC OS.

Previous attempts to bring PMT to RISC OS

Gold

Gold was a project by Acorn to move RISC OS over to the Mach microkernel, which is used today by Apple as the basis of the Darwin kernel used by OS X.

Galileo

Galileo was another project by Acorn to move to a PMT OS, this time from the ground up. Galileo was cancelled with the closure of the workstation division.

Wimp2

Wimp2 used a different approach from previous attempts to build a PMT OS. Rather than build a PMT OS from the ground up, Wimp2 essentially ran inside of the existing OS, as a PMT environment for applications to run in. This approach has some serious issues, however.

More info

• Wikipedia article on preemption
• Wimp2 page
• Microsoft knowledge base article on how multitasking works in Windows 95 (relevant due to similar issues existing between the Windows 3.1 to Windows 95 transition, and a transition from current versions of RISC OS to a PMT version. However, this may not be the best approach.)

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