DOS. Its essence dominated the world and the wills of millions of users for years. We achieved extraordinary things with that family of operating systems (including all developments that didn't come from Microsoft), and it also taught us a new definition of pain. However, there are still details we haven't been able to resolve in these last four decades, and Bryan Lunduke decided to explore one of them: The lack of multitasking in DOS, is it a myth or not? As you can imagine, the answer for the Web is a gigantic “it depends”…
“It was the best of times and it was the worst of times; the age of wisdom and also of madness…”
Dickens gave a true lesson with that opening, but the most striking thing is that it fits the DOS years perfectly. Changes happened at a chilling speed: Everything was new, and in just a blink, the new was already old, replaced by something even newer that was doomed to repeat the cycle. Even so, DOS conveyed rigidity. We learned to use computers, but it was a painful and unforgiving process, with manually edited configuration files, endless documentation, and constant struggles to reclaim kilobytes of conventional memory.
Imagining DOS doing something “different” was not common, and any idea of multitasking belonged to a parallel dimension… but reality indicated otherwise. Regardless of the technical differences between cooperative multitasking and preemptive multitasking, the truth is that there were several special developments with the ability to replicate that multitasking functionality under DOS, and the portal of Bryan Lunduke shows us some of the most relevant examples.
The Quest for Multitasking in DOS
Lunduke's position is clear from the start: DOS could do multitasking, natively in some cases, and with the help of external tools in others. Among the native options, Concurrent DOS stands out, created by Digital Research and Gary Kildall (DR-DOS and GEM also came from there), presented as a “multitasking and multiuser operating system”. However, it would be a mistake not to mention the “MS-DOS 4.0 Multitasking”.
Why is that important? Very simple: Not everyone knows that there were two versions of MS-DOS 4. The most common was the one developed by IBM, which we remember for its infinite number of bugs and compatibility errors. On the other hand, MS-DOS 4.0 Multitasking was a brief Microsoft project that in 1986 included (among other things) true preemptive multitasking. Unfortunately, that system didn't make much noise, but it became a sort of proto-OS/2. The article continues with references to IBM TopView, Quarterdeck DESQview, and a nearly forgotten operating system named Wendin-DOS.
In short, the DOS family was not alien to multitasking. Now, whether we can really call it multitasking or not... that's a doubt that throws us into a much blacker hole than we think. Can a computer with one processor, one core, and one thread do multitasking? Is it valid to talk about multitasking when DOS couldn't even process the concept of a “task”? Comments are open.
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