From: Steve Arnold (steve.arnold4_at_verizon.net)
Date: Tue Jan 06 2004 - 21:19:54 PST
Ritchie and Thompson of Bell Laboratories describe the UNIX operating system
as it was implemented during the PDP-11/45 timeframe. They describe at
length the file system, including how any files are stored (on disk) using
indexes and a hierarchical directory structure. Much time is spent
describing the file system, because almost everything is stored in it,
including "special files" used for reading and writing I/O devices. They
spend some time describing the sytem calls needed for using I/O, as well as
a brief overview of the protection system. They then go on to describe in
more detail how this is implemented logically and technically.
In much briefer sections, they describe other aspects of UNIX. One of which
is processes, noting that machine state is stored in images. It explains how
the shell (interchangeable) can make system calls to basically command the
operating system. Default syntax is given for such features as redirection
and piping. In conclusion, they do a hand wave over performance and explain
its success.
It is quite interesting to me how much has not changed in UNIX. Most of what
they explain in 1974 still holds true for UNIX-based operating systems
today. They do describe some limitations (such as max file size) that are
not realistic for today's computing needs. Given that it has withstood this
30-year test of time, you would have though it would be more scalable from
the beginning. Maybe this is somewhat of result of designing to the hardware
available.
In all, the paper was an excellent UNIX refresher for me, a paper that I
might refer to one who would like some UNIX background. However, I do feel
that they got wrapped up in some of the specifics and could have linked
together some of the big features (such as explaining how processes and
images are essential to multiprogramming). I would also liked to have know
how their version differed from more primitive versions of UNIX and what
have they learned.
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