Mailinglist Archive: opensuse (818 mails)

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Re: [opensuse] different types of shell scripts
Anton Aylward wrote:
Back when, UNIX started something radically different that we now
consider the norm. Back when, processes were deemed expensive to create
so they weren't. The CLI just ran one program at a time, had not
control flow. There was a "Transient Program Area" and the CLI caused
the executive to overlay the CLI with the application. Great for what
were single process systems like CPM/DOS and their mainframe
predecessors. When the application terminated the system somehow
reloaded the CLI and you were off again.

What made UNIX radical was that the CLI, the shell, stuck around;
process creation was cheap an easy and so the application was run in a
sub-process. That meant the CLI could do things that weren't possible
before. It could run a sequence of programs; it could run two (or more)
child processes that were connected via pipe.

We take this for granted now, but back in the 70s and 80s this was
radical.

Hmm, UNIX was first named UNICS, named after MULTICS, from which it took
many features, including multiprocessing. As well as MULTICS, the
Burroughs MCP had parallel execution of tasks, as did ICL's GEORGE 3.
They all had job control languages too, and all in the 1960s before Unix
was conceived.

The history of computing contains a lot of reinventions of the wheel, as
new people join the party or new types of hardware are built. Virtual
memory and filestores are another area where it feels like groundhog day.
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