So Lars Brinkhoff and I were chatting about daemons:
https://gunkies.org/wiki/Talk:Daemon
and I pointed out that in addition to 'standard' daemons (e.g. the printer
spooler daemon, email daemon, etc, etc) there are some other things that are
daemon-like, but are fundamentally different in major ways (explained later
below). I dubbed them 'system processes', but I'm wondering if ayone knows if
there is a standard term for them? (Or, failing that, if they have a
suggestion for a better name?)
Early UNIX is one of the first systems to have one (process 0, the "scheduling (swapping)
process"), but the CACM "The UNIX Time-Sharing System" paper:
https://people.eecs.berkeley.edu/~brewer/cs262/unix.pdf
doesn't even mention it, so no guidance there. Berkeley UNIX also has one,
mentioned in "Design and Implementation of the Berkeley Virtual Memory
Extensions to the UNIX Operating System":
http://roguelife.org/~fujita/COOKIES/HISTORY/3BSD/design.pdf
where it is called the "pageout daemon".("During system initialization, just
before the init process is created, the bootstrapping code creates process 2
which is known as the pageout daemon. It is this process that .. writ[es]
back modified pages. The process leaves its normal dormant state upon being
waken up due to the memory free list size dropping below an upper
threshold.") However, I think there are good reasons to dis-favour the term
'daemon' for them.
For one thing, typical daemons look (to the kernel) just like 'normal'
processes: their object code is kept in a file, and is loaded into the
daemon's process when it starts, using the same mechanism that 'normal'
processes use for loading their code; daemons are often started long after
the kernel itself is started, and there is usually not a special mechanism in
the kernel to start daemons (on early UNIXes, /etc/rc is run by the 'init'
process, not the kernel); daemons interact with the kernel through system
calls, just like 'ordinary' processes; the daemon's process runs in 'user'
CPU mode (using the same standard memory mapping mechanisms, just like
blah-blah).
'System processes' do none of these things: their object code is linked into
the monolithic kernel, and is thus loaded by the bootstrap; the kernel
contains special provision for starting the system process, which start as
the kernel is starting; they don't do system calls, just call kernel routines
directly; they run in kernel mode, using the same memory mapping as the
kernel itself; etc, etc.
Another important point is that system processes are highly intertwined with
the operation of the kernel; without the system process(es) operating
correctly, the operation of the system will quickly grind to a halt. The loss
of ordinary' daemons is usually not fatal; if the email daemon dies, the
system will keep running indefinitely. Not so, for the swapping process, or
the pageout daemon
Anyway, is there a standard term for these things? If not, a better name than
'system process'?
Noel
For the benefit of Old Farts around here, I'd like to share the good
word that an ITS 138 listing from 1967 has been discovered. A group of
volunteers is busy transcribing the photographed pages to text.
Information and link to the data:
https://gunkies.org/wiki/ITS_138
This version is basically what ITS first looked like when it went into
operation at the MIT AI lab. It's deliciously arcane and primitive.
Mass storage is on four DECtape drives, no disk here. Users stations
consist of five teletypes and four GE Datanet 760 CRT consoles (46
colums, 26 lines). The number of system calls is a tiny subset of what
would be available later.
There are more listings from 1967-1969 for DDT, TECO, LISP, etc. Since
they are fan-fold listings, scanning is a bit tricky, so a more labor-
intensive photographing method is used.
Hello everyone, I was wondering if anyone is aware of any surviving technical diagrams/schematics for the WECo 321EB or WECo 321DS WE32x00 development systems? Bitsavers has an AT&T Data Book from 1987 detailing pin maps, registers, etc. of 32xxx family ICs and then another earlier manual from 1985 that seems to be more focused on a technical overview of the CPU specifically. Both have photographs and surface level block diagrams, but nothing showing individual connections, which bus leads went where, etc. While the descriptions should be enough, diagrams are always helpful.
In any case, I've recently ordered a 32100 CPU and 32101 MMU I saw sitting on eBay to see what I can do with some breadboarding and some DRAM/DMA controllers from other vendors, was thinking of referring to any available design schematics of the 321 development stuff for pointers on integrations. Either way, i'm glad the data books on the hardware have been preserved, that gives me a leg up.
Thanks for any insights!
- Matt G.
