they will be quite happy and you don't have much to backup
The above, basically say "if you want to do multitasking on a '51 you need restrict the resources available to each task.

I never said multitasking could not be done on a '51, just that the '51 is the wrong choice for multiprocessing. Especially today, when you can buy an ARM for about the same money.

Now, some will argue that they need some I/O that a '51 derivative has. Fine, but if you need special I/O you are most likely processing something that would die if multitasking was implemented.

Running several simultaneous tasks on '51 is wonderful if you do it with a swarm of processors that each run one task (but that would, of course, be multiprocessing). With sub $1 derivatives available that is a very sound route.

Erik