INTRODUCTION TO OPERATING SYSTEM.

1. OPERATING SYSTEMS
BY L. Mutanu Mwaura

2. CH1: OVERVIEW OF OPERATING SYSTEMS
What is the operating system?
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3. CH1: OVERVIEW OF OPERATING SYSTEMS
• An OS is a program that acts an intermediary
between the user of a computer and computer
hardware.
• Major cost of general purpose computing is
software.
▫ OS simplifies and manages the complexity of
running application programs efficiently.
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4. CH1: OVERVIEW OF OPERATING SYSTEMS
Introduction
• A computer system consists of
▫ hardware
▫ system programs
▫ application programs
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5. CH1: OVERVIEW OF OPERATING SYSTEMS
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6. CH1: OVERVIEW OF OPERATING SYSTEMS
What is the difference between the
OS and the kernel
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7. CH1: OVERVIEW OF OPERATING SYSTEMS
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8. CH1: OVERVIEW OF OPERATING SYSTEMS
Goals of an Operating System
• Simplify the execution of user programs and
make solving user problems easier.
• Use computer hardware efficiently.
▫ Allow sharing of hardware and software resources.
• Make application software portable and
versatile.
• Provide isolation, security and protection among
user programs.
• Improve overall system reliability
 error confinement, fault tolerance, reconfiguration.
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9. CH1: OVERVIEW OF OPERATING SYSTEMS
• Can the computer run without an
operating system?
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10. CH1: OVERVIEW OF OPERATING SYSTEMS
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Without an OS the computer functions would not
be synchronized!

11. CH1: OVERVIEW OF OPERATING SYSTEMS
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12. Systems Today Compiled by L. Mutanu
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13. Irvine Sensorium
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14. CH1: OVERVIEW OF OPERATING SYSTEMS
Hardware & Software Complexity IncreasesCompiled by L. Mutanu
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Moore’s Law: 2X
transistors/Chip Every 1.5 years
Moore’s Law

15. CH1: OVERVIEW OF OPERATING SYSTEMS
1985 - Windows 1.0
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Windows 2.0
Windows 3.0
Windows 3.1
Windows 95
Windows 98
Windows 2000
Windows ME
Windows XP
Windows 7
Windows Vista

16. CH1: OVERVIEW OF OPERATING SYSTEMS
What is your preferred operating
system?
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17. CH1: OVERVIEW OF OPERATING SYSTEMS
Examples of operating systems
• Open source - Based on open, published source code
▫ UNIX and Linux
• Proprietary - Closed
▫ Apple Macintosh
• Hybrid - Some elements open, some elements closed
▫ Microsoft
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18. CH1: OVERVIEW OF OPERATING SYSTEMS
Early Systems - Bare Machine (1950s)
• Structure
 Large machines run from console
 Single user system
 Programmer/User as operator
 Paper tape or punched cards
• Early software
 Assemblers, compilers, linkers, loaders, device drivers, libraries of
common subroutines.
• Secure execution
• Inefficient use of expensive resources
 Low CPU utilization, high setup time.
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Hardware – expensive ; Human – cheap

19. CH1: OVERVIEW OF OPERATING SYSTEMS
1. Simple Batch Systems (1960’s)
• Reduce setup time by batching jobs with similar requirements.
• Add a card reader, Hire an operator
▫ User is NOT the operator
▫ Automatic job sequencing
 Forms a rudimentary OS.
▫ Resident Monitor
 Holds initial control, control transfers to job and then back to monitor.
▫ Problem
 Need to distinguish job from job and data from program.
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20. CH1: OVERVIEW OF OPERATING SYSTEMS
▫ Problem with Batch Systems
 Long turnaround time - up to 2 DAYS!!!
 Low CPU utilization - I/O and CPU could not overlap;
▫ Solutions to speed up I/O:
▫ Offline Processing
 load jobs into memory from tapes, card reading and line printing are
done offline.
▫ Early batch system
 bring cards to 1401
 read cards to tape
 put tape on 7094 which does computing
 put tape on 1401 which prints output
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21. CH1: OVERVIEW OF OPERATING SYSTEMS
2. Multiprogramming
• Keep more than one running job in
memory. When one job waits for IO,
switch to a different job
• Use interrupts to run multiple
programs concurrently
 When a program performs I/O, instead
of polling, execute another program till
interrupt is received.
• Time sharing was introduced. - Like
multiprogramming, but timer device
interrupts after a quantum (timeslice).
 Interrupted program is returned to end
of FIFO
 Next program is taken from head of
FIFO
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22. CH1: OVERVIEW OF OPERATING SYSTEMS
• Multiprogramming increased efficiency and time
sharing increased convenience. However with this
came along certain challenges:
▫ a single process might monopolize CPU or memory
▫ One process might overwrite another’s memory
▫ If total program memory exceeds system memory,
there is need for additional memory
▫ The System state (program counter, registers, etc)
needs to be saved and restored on every job switch
• Certain features needed to be added to the OS to
solve these challenges. Result: added complexity
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23. CH1: OVERVIEW OF OPERATING SYSTEMS
• Certain additional OS Features were required for
Multiprogramming
▫ I/O routine supplied by the system.
▫ Memory management – the system must allocate the
memory to several jobs. Virtual Memory - Not all of the
program’s has to be resident at once in primary memory.
Requires the use of secondary memory the translation of
memory references into real hardware addresses.
▫ CPU scheduling – the system must choose among several
jobs ready to run.
▫ Allocation of devices.
▫ Interactive Computing - On-line communication between
the user and the system is provided; when the operating
system finishes the execution of one command, it seeks the
next “control statement” from the user’s keyboard.
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24. CH1: OVERVIEW OF OPERATING SYSTEMS
3. Personal Computing Systems
• Single user systems, portable, GUI.
• I/O devices - keyboards, mice, display screens, small printers.
• Laptops and palmtops, Smart cards, Wireless devices.
• Single user systems may not need advanced CPU utilization or
protection features.
• Advantages:
▫ user convenience, responsiveness, ubiquitous
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Hardware – cheap ; Human – expensive

25. CH1: OVERVIEW OF OPERATING SYSTEMS
4. Parallel Systems
• Multiprocessor systems with more than one CPU in close
communication.
• Improved Throughput, economical, increased reliability.
• Kinds:
 Symmetric and asymmetric multiprocessing
 Distributed memory vs. shared memory
• Advantages of parallel system:
▫ Increased throughput
▫ Increased reliability - fail-soft systems
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26. CH1: OVERVIEW OF OPERATING SYSTEMS
5. Distributed Systems
• Distribute computation among many processors.
• Loosely coupled -
 no shared memory, various communication lines
• client/server architectures
• Advantages:
 resource sharing
 computation speed-up
 reliability
 communication - e.g. email
• Applications - digital libraries, digital multimedia
• Two types of system architectures exist:
▫ Client-server systems place shared
resources on centralized servers
▫ Peer-to-peer systems allow ad-hoc
cooperation between individuals
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Hardware – very cheap ; Human – very expensive

27. CH1: OVERVIEW OF OPERATING SYSTEMS
6. Real-time systems
• Correct system function depends on timeliness
• Feedback/control loops
• Sensors and actuators
• Hard real-time systems -
 Failure if response time too long.
 Secondary storage is limited
• Soft real-time systems -
 Less accurate if response time is too long.
 Useful in applications such as multimedia, virtual reality.
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28. CH1: OVERVIEW OF OPERATING SYSTEMS
• Many different operating system models have
evolved over time, driven by
▫ Hardware costs
▫ Efficiency
▫ Convenience for the user
• Today we have Personal Digital Assistants (PDAs)
and Cellular telephones. Research is still in process
to develop operating systems that can curb issues
such as:
▫ Limited memory
▫ Slow processors
▫ Small display screens.
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29. Current OS Technology
Personal digital assistant
(PDA)
iPad/Tablet
video phone
Laptop
Robots
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30. Future OS Technology?
Wearable or
luggable?
LCD
Jacket
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33. CH1: OVERVIEW OF OPERATING SYSTEMS
Intelligent Environment
• Lights, air conditioning, TV automatically switch on and off when you enter or
leave rooms
• Sit on your favourite chair and TV switches on to the program you usually
watch at this time of the day
• Use communicator/pda for phone, remote control, keys
payments, passport, health records, authenticator.
• Route input from ‘virtual’
keyboard to nearest suitable
display.
• Automatic detection of new
items to control and physical
layout in a room or office, using
computer vision.
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34. CH1: OVERVIEW OF OPERATING SYSTEMS
Intelligent Environment
• Fridge and cupboards tracks consumption and reorder your
groceries
• Your car computer reminds you to pick up your order on the way
home when you are near the supermarket.
• Interesting, but can you foresee any challenges with such an
OS?
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35. CH1: OVERVIEW OF OPERATING SYSTEMS
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36. CH1: OVERVIEW OF OPERATING SYSTEMS
Summary history of Operating Systems
• First generation 1945 - 1955
▫ Manual Operators
• Second generation 1955 - 1965
▫ OS introduced for Job Sequencing
• Third generation 1965 – 1980
▫ Multiprogramming introduced
• Fourth generation 1980 – present
▫ personal computers
▫ Multiprocessing
▫ Distributed Systems
▫ Real Time Systems
▫ Embedded operating systems
▫ Smart card operating systems
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37. CH1: OVERVIEW OF OPERATING SYSTEMS
People-to-Computer Ratio Over Time
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38. CH1: OVERVIEW OF OPERATING SYSTEMS
Why should I study Operating Systems?
▫ Need to understand interaction between the hardware
and applications
 New applications, new hardware..
 Inherent aspect of society today
▫ Need to understand basic principles in the design of
computer systems
 efficient resource management, security, flexibility
▫ Increasing need for specialized operating systems
 e.g. embedded operating systems for devices - cell
phones, sensors and controllers
 real-time operating systems - aircraft control, multimedia
services
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