Section A.
INTRODUCTION TO UNIX
The Operating System
Unix is a multiuser, timesharing/multi-tasking, and remarkably
open system that allows for simple file sharing capability among
users. All input and output (I/O) is streams (sequences of
characters followed by the end-of-text character), rather than
records. Files are named streams and are randomly addressable. A
particular type of file, a directory, provides mapping between
names of ordinary files and their physical existence on disk. The
filesystem forms an inverted tree structure, the root directory
(/) being the topmost level, with sub-directories branching below.
Files may reside at any level of the directory tree. Links to a
file by the same or different names may exist in several
directories. Devices (terminals/printers) have associated with
them a special file, usually found in the directory /dev, and I/O
is done exactly as with ordinary files, except that the device is
also activated. Pipes (|) allow directing output from one command
to another via a buffer (a temporary storage area) without making
any changes to the command.
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