DOS ain't dead

> According to you, what is the best way to ignore entirely these 3 specific
> keyboard entries, which light up a led : caps lock, num lock, screenPause?
>
> I know that these keys are specific as their treatment takes some CPU time,
> which is precisely my problem. So is it possible for MSDOS to ignore this?

DOS doesn't normally handle the keyboard, it lets the BIOS do it instead. The keys you specifically mentioned are not normally processed by DOS at all, and I've never seen a BIOS that would let you "ignore" them. But, DOS will let you redefine key(s) to do something other than what the BIOS normally does.

If you're unwilling to write a custom program yourself, there are a couple of options you can try. The first is the FreeDOS KEYB program:

http://www.ibiblio.org/pub/micro/pc-stuff/freedos/files/dos/keyb/2.01/

I'm not sure if it will let you redefine a key to do nothing at all, but it should let you redefine a key to do something innocuous (like a <Shift> key or <Escape> key or something).

You could also try my SCANCODE program:

http://bretjohnson.us

SCANCODE is sort of like a programmable macro facility, that let's you "type" keys into other programs in response to different input parameters (timing, text {dis}appearing on screen, time of day, other keystrokes, etc.). One of the things it can do is effectively change one key into another, so it could be used to change your special keys into something innocuous as well, such as beeping the speaker. It can also be used to effectively disable the entire keyboard for a period of time, though I'm not sure that's what you're after.

Since timing is your main concern, your best option is probably to write a custom program.