Download CSC 150 UNGRADED QUIZ - Concordia University Wisconsin

SYSTEMS SOFTWARE II
(1) Review of operating systems (O/S)
basics.
(2) O/S components in depth:
(a) user interface,
(b) application interface,
(c) resource manager.
1. Review of operating systems.
 A. Definition. An operating system is a
master control program which controls all
the H/W and other software of a computer
system.
 B. Analogies for an O/S.
 “General manager,”
 “traffic cop,” “steward,” “shepherd.”
2. O/S components in more
depth.
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Jobs of the O/S include:
1) user interface,
2) application interface,
3) resource manager.
See full diagram.
2A. User interface.
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1) allows user to communicate with H/W
2) made possible by a command interpreter.
In DOS or UNIX, command-line entry.
In Windows or XWindows, the operating
system is enhanced by a graphical
operating environment, which means one
can issue commands without naming them.
Comparison of DOS and
Windows for listing files.
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DOS.
C:> cd mystuff
C:\mystuff> dir
Windows.
Icons on desktop, My Computer and
Windows Explorer, visual means of
navigating, copying, moving, deleting.
User interface continued.
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Advantage of command line approach?
Very efficient, complete control to user.
Disadvantage?
Must memorize commands, know how to
“program” in the language of the O/S.
User interface continued.
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Four main Types of command:
A. Resident / internal commands.
-- Always in RAM.
-- Protected from being overwritten.
-- Frequently used or essential.
E.g. everything necessary to list directories
or print.
User interface continued.
 B. Transient / external commands.
 -- Held on auxiliary storage until needed.
 -- Loaded into unprotected memory (can
be overwritten).
 -- Less often used commands e.g. format.
 C. Executables. E.g. .EXE, .COM
 D. Batch / Script files. .BAT
2B. Application program
interface.
 S/W is not allowed to directly control H/W.
Instead it makes requests to use the H/W via
the operating system. The operating
system is the “proper channel” or
mediator.
 Theological parallel: No-one can come to
the Father except through Christ.
 “No program can come to the H/W except
through the O/S.” [Ideally, anyway.]
User interface continued.
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Why?
1) Makes applications more efficient,
2) Makes applications more portable,
3) Protects the hardware from conflicts.
Applications, like individual humans,
cannot see the whole picture. Like a “god,”
the O/S can see the whole picture and avoid
conflicts.
User interface continued.
 2C. Resource manager.
 In typical computer systems, there is always
competition for resources. To avoid
conflicts and to allow fair usage, resource
management is needed for the 4 main
resources:
 (1) MEMORY, (2) PROCESSOR,
 (3) FILES,
(4) DEVICES.
(1) Memory manager.
 Jobs:
 Allocates and deallocates memory (RAM)
for programs and data;
 Avoids conflicts (protects O/S and
application instructions and data);
 Creates virtual memory, e.g. in Windows by
demand paging.
 Creates illusion we have more memory than
we do.
(2) Processor manager.
 Jobs:
 Allocates and deallocates CPU to
applications.
 Allows time sharing schemes.
 1. Multiprogramming: many users share
one CPU, e.g. on a mainframe.
 2. Multitasking: one user has many
applications open at the same time.
Requires “reentrant code.”
Processor manager.
 3. Multithreading: a single program is
divided up into threads which can be
updated independently e.g. JAVA applets.
(3) File manager.
 Jobs:
 Creates illusion that files are organized
logically even though they are physically
stored in fragments (“extents” of “noncontiguous” storage).
 Maintains locations of files.
 Maintains access rights. Ro, Rw, C, E
 Interfaces with Device manager.
(4) Device manager.
 Jobs:
 Controls peripherals (devices outside
processor unit, i.e. auxiliary storage and
I/O).
 Avoids conflicts of non-shareable resources
 e.g. Printers / plotters.