operating systems

1. Operating Systems
Course: B.Sc-CS
Subject: Fundamental Of Information Technology
Unit: 3

2. Operating System Software
• Operating System (OS) – Software that controls the overall operation of a
computer
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3. What is an operating system (OS)?
Operating System Software
Software which manages the overall operation of the computer system including:
• hardware (CPU, RAM, I/O)
• security
• system interface
• application interface
3

4. The functions of an operating system
1. Manages and Interacts with Computer
Hardware
2. Provides and Manages System Security
3. Provides the System Interface
4. Provides the Interface for Application
Software
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5. 1. Manages and Interacts with Computer Hardware
• Manages the CPU
- What software programs the
CPU works on and when
• Manages RAM
- What is stored in RAM and
where it is stored
- Virtual memory
- OS will send message when
RAM is full
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6. 1. Manages and Interacts with Computer Hardware (continued)
• Provides the interface for storage
devices and manages how data is
stored on those devices
- in charge of formatting disks
- creates sectors and clusters
- creates F.A.T. or V.T.O.C.
- sends message when disk is
full or there is some other
problem with writing data to
the disk
- virtual memory
- CD-ROM, DVD-ROM
- Flash drive
6

7. 1. Manages and Interacts with Computer Hardware (continued)
• Provides the Interface for Input and
Output Devices
– keyboard, mouse, printer,
– device drivers = software
programs which allow the
hardware device to be used by
the operating system and by
application software
Rick Graziani graziani@cabrillo.edu 7

8. 2. Provides and Manages System Security
Single-user Operating Systems
• minimal security
• user has full authority
Server Operating Systems
• login and password capability
• protection of user’s data stored
on the server’s central hard disk
drives
• protection and security for
software programs
Rick Graziani graziani@cabrillo.edu 8

9. 3. Provides the System Interface
System Interface or shell =
the interface between the
user and the computer
Command Line Interface
(CLI)
• Linux, UNIX, DOS, older
OS’s
Graphical User Interface
(GUI)
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10. 4. Provides the Interface for Application Software
• Operating systems are
software
• Operating systems are
designed and developed for a
specific CPU or “family of
CPUs”
– Macintosh OS: Motorola
680xx, PowerPC Gx, Intel
– DOS: Intel CPUs
– Windows 9x and XP: Intel
80386, 80486, and Pentium
CPUs
– Linux: Intel CPUs
– MS NT & 2000: Intel CPUs
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11. 4. Provides the Interface for Application Software
(continued)
• Application software is developed
for an operating system
MS Word for Windows XP
• Windows XP
• Intel CPU
MS Word for the Macintosh
• Macintosh OS X
• Gx CPU or Intel CPU
11

12. Order of Development
1. The CPU
2. Other Hardware
Components
3. Operating System
Software
4. Application Software
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13. Types of Operating System

14. Architecture of Computer System
Hardware
Operating System (OS)
Programming Language (e.g. PASCAL)
Application Programs (e.g. WORD, EXCEL)

15. Operating System
• a collection of programs which control the
resources of a computer system
• written in low-level languages (i.e. machine-
dependent)
• an interface between the users and the
hardware
• when the computer is on, OS will first load
into the main memory

16. Operating
System
Device configuration
Controls peripheral devices connected to the computer
File management
Transfers files between main memory and secondary storage,
manages file folders, allocates the secondary storage space,
and provides file protection and recovery
Memory management
Allocates the use of random access memory (RAM) to
requesting processes
Interface platform
Allows the computer to run other applications
Basic functions of the operating system

17. Other function of Operating System
• best use of the computer resources
• provide a background for user’s programs to
execute
• display and deal with errors when it happens
• control the selection and operation of the
peripherals
• act as a communication link between users
• system protection

18. Common Operating Systems and Their
Differences
• Network Operating System
– UNIX / Linux / MS Windows2000 Server
• Desktop Operating System
– MS Windows 9X/Me / Mac OS / DOS
• Mobile Operating System
– Palm OS and Pocket PC

19. Different Features of Operating System

20. Type of Operating System
• Batch processing
• Real time processing
• Time sharing processing

21. Batch processing
• Jobs, together with input data, are fed into
the system in a batch.
• The jobs are then run one after another.
• No job can be started until previous job is
completed

22. Real time processing
• immediate response is needed.
• For example
– anti-missile defense system
– airplane landing control system
– interrupt error in computer system

23. Time sharing processing
• Each user is given a time slice to interact
with the CPU.
• The size of the time slice will depend on the
system.
• Each user is served in sequence.

24. Special Features of OS
• multi-tasking
• multi-programming
• parallel processing
• buffering
• spooling

25. Multi-tasking
• to handle 2 or more programs at the same time
from a single user ‘s perception
– CPU can only perform one task at a time, however,
it runs so fast that 2 or more jobs seem to execute
at the same time

26. Multi-programming
• 2 or more programs store in the main memory
at the same time
• when one job reeds to wait (e.g. I/O operation),
CPU switch to another job to execute
• when the first job finishes waiting, CPU will
get back the first job to execute

27. Parallel Processing
• use 2 or more CPUs to handle jobs
• computer networking
Job 1 Job 2
Job 3
Job 4
Job 1
Job 2
Job 3
Job 4
CPU 1 CPU 2 CPU 1
time time
without multiprocessing
with multiprocessing

28. Buffering
• A temporary storage area (buffers) to read data
from input device or send data to the output
device
• keep CPU busy
– because I/O operation is slow

29. Reference
Book Reference
1. Operating System Concepts by Abraham Silberschatz, Peter B. Galvin, Greb
Gagne
2. Operating System Concepts by James Lautor Peterson, Abrahamautor Silbeschatz
3. Database System Concepts by Abraham Silberschatz, Henry F. Korth,
S.Sudarshan
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