The Amiga wasn't the first to do two things at once

It is a line you hear a lot: the Amiga, from 1985, was the first home computer with multitasking. The AmigaOS kernel, Exec, written by Carl Sassenrath, did indeed do preemptive multitasking, in which it is the system, not the program, that decides when each task runs, and it did it in just 256 KB of memory ^[1]. But others got there first.

By the end of 1983, Radio Shack was already selling OS-9 Level I, from Microware, for its TRS-80 Color Computer. The Tandy manual explained: "Multitasking means that two or more tasks (programs) can run at the same time. For example, with OS-9 you could print reports and enter information at the same time" ^[2]. The same manual describes time divided into slices between clock ticks, and on each tick the system can suspend one process and hand over to another ^[2]. OS-9 used priority-based preemptive scheduling, and the CoCo, cheap and a big seller, was the machine where it became best known ^[3].

The first home multitasking was not the Amiga's: it was already running on a Tandy in 1983 and on a Sinclair in 1984.

In January 1984, Sinclair unveiled the QL, with Tony Tebby's QDOS in ROM: a preemptive multitasking system, which Sinclair advertised as the first on a mass-market computer ^[4]. Deliveries only began in April, but even so the QL arrived more than a year before the Amiga ^[4]. One QL owner was a young Finn called Linus Torvalds, who liked precisely the machine's preemptive multitasking ^[4].

What the Amiga brought was preemptive multitasking as standard from day one, 23 July 1985: a kernel of just 13 KB, with priorities and message passing between tasks, very efficient because they all share the same memory space ^[1]. There was a catch: with no memory protection, a badly behaved program could switch multitasking off at will and freeze everything else ^[1].

To get an idea of the lead, the Macintosh only gained MultiFinder in August 1987, and even then with cooperative multitasking, in which each program has to give up the processor of its own accord. The classic Mac never had preemptive multitasking: it only got it with Mac OS X ^[5].