William Hern
Member
The original vision for the Macintosh project, when it was led by Jef Raskin, was for a low cost $500 computer. It would have featured the 8 bit 6809 processor (with a 64K memory limit) running at perhaps 2 MHz, so multi-tasking was not viable for memory and performance reasons.
Leaving aside the matter of whether or not the Lisa had true pre-emptive multitasking (I'd argue that it was more akin to co-operative multitasking), implementing pre-emptive multitasking was non-trivial in the early 80s. It requires memory protection hardware (to avoid software programmes trampling all over each other), which Motorola didn't support for the 68000 - companies had to design their own hardware to do this. Furthermore the operating system needs to be written carefully to support multitasking and provide the illusion to a software programme that it is the only thing running. Pre-emptive task scheduling is complex to implement and must be written very efficiently.
To answer the final part of your question: Multitasking, like security, is hard to retrofit. No unitasking operating system was successfully converted to be multitasking, as far as I know. Windows 9x provided some degree of multitasking but proper pre-emptive multitasking didn't arrive until Windows NT, which was a written from scratch, and designed from Day 1 to be multi-tasking.
Leaving aside the matter of whether or not the Lisa had true pre-emptive multitasking (I'd argue that it was more akin to co-operative multitasking), implementing pre-emptive multitasking was non-trivial in the early 80s. It requires memory protection hardware (to avoid software programmes trampling all over each other), which Motorola didn't support for the 68000 - companies had to design their own hardware to do this. Furthermore the operating system needs to be written carefully to support multitasking and provide the illusion to a software programme that it is the only thing running. Pre-emptive task scheduling is complex to implement and must be written very efficiently.
To answer the final part of your question: Multitasking, like security, is hard to retrofit. No unitasking operating system was successfully converted to be multitasking, as far as I know. Windows 9x provided some degree of multitasking but proper pre-emptive multitasking didn't arrive until Windows NT, which was a written from scratch, and designed from Day 1 to be multi-tasking.