Talk:Daemon

Demon, dragon, phantom

I'd like to expand the discussion on this page, or create a separate page, to include the usage of demon on ITS, and also the related dragon. On WAITS, there's a related phantom concept which I don't really know but I intend to find out. Since these are all various form of system background processes, they are similar and so might be best discusses in a single place. Or there could be separate pages for each. Having typed all this, I now figure I should just go ahead and then we can move things around later. Ok, thanks for reading! Larsbrinkhoff (talk) 07:40, 14 August 2023 (CEST)

Yeah, they are all basically the same thing, so cover them all in one page.

The only technical difference worth noting is between 'classic' daemons, such as line printer and email daemons, and what I seem to recall are called 'system processes', which are key parts of the OS itself, and in the case of the Unix 'swapping' process, live entirely in the kernel and never run in 'user' mode. That process doesn't get its code from a file; its code is built into the kernel, and so is loaded at the same time, and by the same mechanism, as the kernel itself.

Those would be worth a separate page, if we can find a 'usual' term for such things. The Unix CACM paper doesn't mention it; a comment in the code calls it the "scheduling (swapping) process". I vaguely recall the term 'system process' being used for such things, but I do not remember where from.

I think the ITS 'CORE JOB' might be in this category (and I seem to recall the code for it is in SYSENG;); do you know more about it? I have this vague memory that it writes 'dirty' pages out, to maintain a free list. (Multics has a similar concept, IIRC; it's covered in the Multics Storage System Program Logic Manual. Without looking, I don't recall if it's done as a process, or if Multics just writes dirty pages as part of the page fault code.)

What does the 'SYS SYS' job in ITS do? Is it just an idle process? (The PDP-10 doesn't have a WAIT instruction, the way the PDP-11 does, I am pretty sure.) I think Puff just keeps records of command usage - or am I confused? COMSAT was more of a classic daemon.

I don't recall the term 'demon' ever being used for any of these things. Ever since 'daemon' was adopted under CTSS, that was the term. (Someone who'd heard it used, but never seen it, might have used the incorrect spelling.) Jnc (talk) 15:12, 14 August 2023 (CEST)