p1

unix v7是最后一个广泛发布的研究型UNIX版本

.ds n \s+2
.hw above-mentioned
.ds s \s-2
.ds m \v'-.3'.\v'.3'
.TL
The UNIX
Time-Sharing System\f1\s10\v'-.2n'*\v'.2n'\s0\fP
.AU
D. M. Ritchie and K. Thompson
.AB
.FS
* Copyright 1974,
Association for Computing Machinery, Inc.,
reprinted by permission.
This is a revised version of an article
that appeared in Communications of the \*sACM\*n,
.IT 17 ,
No. 7 (July 1974), pp. 365-375.
That article was a
revised version of a paper presented
at the Fourth \*sACM\*n Symposium on Operating
Systems Principles,
\*sIBM\*n Thomas J. Watson Research Center,
Yorktown Heights,
New York,
October 15-17, 1973.
.FE
.UX
is a general-purpose, multi-user, interactive
operating system for the larger Digital Equipment Corporation
\*sPDP\*n-11 and
the Interdata 8/32 computers.
It offers a number of features
seldom found even in larger operating
systems, including
.IP i
A hierarchical file system incorporating
demountable volumes,
.IP ii
Compatible file, device, and inter-process I/O,
.IP iii
The ability to initiate asynchronous processes,
.IP iv
System command language selectable on a per-user basis,
.IP v
Over 100 subsystems including a dozen languages,
.IP vi
High degree of portability.
.LP
This paper discusses the nature
and implementation of the file system
and of the user command interface.
.AE
.NH
INTRODUCTION
.PP
There have been four versions of
the
.UX
time-sharing system.
.hy 12
The earliest (circa 1969-70) ran on
the Digital Equipment Corporation \*sPDP\*n-7 and -9 computers.
The second version ran on the unprotected
\*sPDP\*n-11/20 computer.
The third incorporated multiprogramming and ran
on the \*sPDP\*n-11/34, /40, /45, /60, and /70 computers;
it is the one described in the previously published version
of this paper, and is also the most widely used today.
.hy 14
This paper describes only the
fourth, current
system that runs on the \*sPDP\*n-11/70 and the
Interdata 8/32 computers.
In fact, the differences among the various systems is
rather small;
most of the revisions made to the originally published version of this
paper,
aside from those concerned with style,
had to do with details of the implementation of the file system.
.PP
Since
\*sPDP\*n-11
.UX
became operational
in February, 1971,
over 600 installations have been put into service.
Most of them are engaged in applications such as
computer science education,
the preparation and formatting of documents
and other textual material,
the collection and processing of trouble data
from various switching machines within the Bell System,
and recording and checking telephone service
orders.
Our own installation is used mainly for research
in operating systems, languages,
computer networks,
and other topics in computer science, and also for
document preparation.
.PP
Perhaps the most important achievement of
.UX
is to demonstrate
that
a powerful operating system for interactive use
need not be expensive either in equipment or in human
effort:
it
can run on hardware costing as little as $40,000, and
less than two man-years were spent on the main system
software.
We hope, however, that users find
that the
most important characteristics of the system
are its simplicity, elegance, and ease of use.
.PP
Besides the operating system proper, some major programs
available under
.UX
are
.DS
.nf
C compiler
Text editor based on \*sQED\*n
.[
qed lampson
.]
Assembler, linking loader, symbolic debugger
Phototypesetting and equation setting programs
.[
cherry kernighan typesetting mathematics cacm
.]
.[
kernighan lesk ossanna document preparation bstj
%Q This issue
.]
.fi
.in +3n
.ll -5n
.ti -3n
Dozens of languages including
Fortran 77, Basic, Snobol, \*sAPL\*n, Algol 68, M6, \*sTMG\*n, Pascal
.in
.ll
.DE
There is a host of maintenance, utility, recreation and novelty programs,
all written locally.
The
.UX
user community, which numbers in the thousands,
has contributed many more programs and languages.
It is worth noting that the system is totally self-supporting.
All
.UX
software is maintained on
the
system;
likewise, this paper and all other
documents
in this issue
were generated and formatted by the
.UX
editor and text formatting
programs.
.SH
II. HARDWARE AND SOFTWARE ENVIRONMENT
.PP
The \*sPDP\*n-11/70 on which the Research
.UX
system is installed is a 16-bit
word (8-bit byte) computer with 768K bytes of core memory;
the system kernel
occupies 90K bytes
about equally divided between code
and data tables.
This system, however, includes a very large number of
device drivers
and enjoys a generous allotment
of space for I/O buffers and system tables;
a minimal system capable of running the software
mentioned above can
require as little as 96K bytes
of core altogether.
There are even larger installations;
see the description of the
\*sPWB/UNIX\*n systems,
.[
dolotta mashey workbench software engineering
.]
.[
dolotta haight mashey workbench bstj
%Q This issue
.]
for example.
There are also much smaller, though somewhat restricted,
versions of the system.
.[
lycklama microprocessor bstj
%Q This issue
.]
.PP
Our own \*sPDP\*n-11 has two
200-Mb moving-head disks
for file system storage and swapping.
There are 20 variable-speed
communications interfaces
attached to 300- and 1200-baud data sets,
and an additional 12 communication lines
hard-wired to 9600-baud terminals and
satellite computers.
There are also several 2400- and 4800-baud
synchronous communication interfaces
used for machine-to-machine file transfer.
Finally, there is a variety
of miscellaneous
devices including
nine-track magnetic tape,
a line printer,
a voice synthesizer,
a phototypesetter,
a digital switching network,
and a chess machine.
.PP
The preponderance of
.UX
software is written in the
abovementioned C language.
.[
c programming language kernighan ritchie prentice-hall
.]
Early versions of the operating system were written in assembly language,
but during the summer of 1973, it was rewritten in C.
The size of the new system was about one-third greater
than that of the old.
Since the new system not only became much easier to
understand and to modify but also
included
many functional improvements,
including multiprogramming and the ability to
share reentrant code among several user programs,
we consider this increase in size quite acceptable.
.SH
III. THE FILE SYSTEM
.PP
The most important role of
the system
is to provide
a file system.
From the point of view of the user, there
are three kinds of files: ordinary disk files,
directories, and special files.
.SH
3.1 Ordinary files
.PP
A file
contains whatever information the user places on it,
for example, symbolic or binary
(object) programs.
No particular structuring is expected by the system.
A file of text consists simply of a string
of characters, with lines demarcated by the newline character.
Binary programs are sequences of words as
they will appear in core memory when the program
starts executing.
A few user programs manipulate files with more
structure;
for example, the assembler generates, and the loader
expects, an object file in a particular format.
However,
the structure of files is controlled by
the programs that use them, not by the system.
.SH
3.2 Directories
.PP
Directories provide
the mapping between the names of files
and the files themselves, and thus
induce a structure on the file system as a whole.
Each user has a directory of his own files;