The Wednesday 2003-11-19 at 16:45 -0500, Jerry Feldman wrote:
Dos 5 or 6 (not sure) included a task manager shell that could run several programs, and switch between them - instead of using windows 3.x - but it was even more unstable than windows. There were commercial programs, like sidekick, that could give the appearance of multi-tasking.
Ah, yes. But the one I meant was part of the system, I mean, it was a MS app, and quite promissing... but not fully. A sophisticated task swapper. I'd have to boot up my other computer in dos 6 to check it, but I'm lazy :-)
However, DOS 5 and 6 were incapable of multi-tasking per se. It used a facility called Terminate and Stay Resident, where a task would tell DOS it was terminating, but not to free up its memory. That task would use some facility, such as an interrupt to gain control. However this was very dangerous, and the programmers had to jump through hoops to prevent from corrupting DOS. (I wrote an SNMP agent. Even calling time would cause DOS to hang.
I know. I once programmed a TSR, but mostly what I did was download most of a program, swapping itself to disk, and call another one. To do simple things like playing a background sound or printing at the same time as the user continued working needed hooking the timer interrupt, checking that dos wasn't busy (not reentrant) before reading the data from disk, etc. And I could never be sure that it wouldn't sometime crash: I just had to hope it didn't do it when showing to clients. Horrible. Brrr! (shudder) As I said, what I liked of Linux when I met it, was that it allowed me to do things that I always wanted to do, and that I knew "serious" computers did. But I don't program now for a living, so I can't say I can program in Linux. Too fast a target, also. -- Cheers, Carlos Robinson