Outcome 1:

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Outcome 1

• Describe the structure and function of an
  operating system.

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Systems Software
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Examples of Software types

• Applications Software
• Word Processor, Spreadsheet, Database, Desktop
  Publishing
• Systems Software
• Compilers, Interpreters
• System utilities
• Operating systems

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Operating Systems

• An operating system is a collection of system
  programs that together control, manage and
  monitor the operation of a computer system.
• Examples
• Controls the execution of applications software
• Controls the operation of the hardware
• Monitors the use of the hardware
• Provides a user-interface

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Operating System
An operating system can be regarded as providing
a layer between the user, applications and the
underlying hardware.
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Types of Operating Systems

• General Purpose
• Used in computers.
• Provide the ability to run a number of different
  applications.
• Examples all versions of Windows
• Embedded Systems
• Do not manage user programs at all
• Perform a well-defined task, usually in a
  real-time environment
• Used to control hardware devices such as cars,
  electronic appliances etc.
• Examples DVD players, car fuel injection etc.

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Types of Operating Systems
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Types of Operating Systems

• Single-user, single-tasking Example MS-DOS
• Single-user, multi-tasking Example Windows XP
• Multi-user, multi-tasking Example Linux
• Real-time Example OSE, QNX

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Functional Areas of an OS.
Input Output
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The Kernel

• Part of the O/S that is responsible for process
  management, multi-tasking and interrupt handling.
• Loads and runs other parts of the o/s when
  required.
• Must reside permanently in memory during computer
  operation.

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Processes

• Process
• A program in execution.
• The OS maintains additional information about
  running programs (location in memory, stack
  pointer, program counter).
• When a program is run, the operating system
  converts it into a process. It is the process,
  rather than the simple program, that the
  processor executes.
• Foreground Process
• A process that currently uses the screen and
  keyboard
• Background Process
• A process that does not require access to the
  screen and keyboard

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The Boot Process

• The core of an OS (known as the kernel) must be
  present in main memory.
• At power-on,
• the basic hardware is checked (POST)
• The video display is enabled
• ROMs found on adapter cards are executed
• A bootable drive is searched for and when found
  its volume boot record loads the OS kernel.
• The kernel then loads and prepares the remainder
  of the O/S.

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The Boot Process

• These power-on activities are carried out by the
  boot program.
• This program is held on ROM (in the BIOS chip) on
  the motherboard.

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Storage of the Operating System

• Storage of an O/S in a computer system may be
  either on
• ROM chip
• Or
• Hard Disk

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ROM based O/S

• The operating system is held on a ROM chip.
• The ROM is configured as part of the main memory.
• Advantages
• The O/S is immediately in control at power up.
• Cannot be corrupted
• Disadvantage
• Updates to O/S require replacement of ROM chip
• Most usually found in embedded systems.

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Disk based O/S

• The O/S must be loaded from disk into main memory
  when the computer is powered up. This is called
  booting the O/S.
• Advantages
• The O/S is easily updated
• No limit to the size of the O/S
• Disadvantages
• The O/S is easily corrupted
• Loading of the O/S may take a considerable time.

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Single-user, single-tasking O/S

• Definition O/S that allows a single user to
  carry out a single task at any one time.

CPU Only one program is allowed to run on the
CPU at any one time. Programs must run to
completion. Memory Only the currently running
program can reside in memory. It has access to
all of memory (apart from the O/S)
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Single-user, single-tasking O/S
I/O The currently running program is given full
dedicated access to all I/O devices. Security Ve
ry few security measures are required.
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Single-user, multi-tasking O/S

• Definition O/S that allows a single user to
  carry out a one or more tasks at any one time.

CPU Programs compete to run on the CPU. The O/S
multi-tasks the programs giving the appearance
that programs are running simultaneously.
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Single-user, multi-tasking O/S
Memory Programs compete for access to memory.
The currently running program must be in memory.
Other programs may be swapped to disk to make
room. I/O Some devices can be shared by
multi-tasking programs (e.g. hard disks). Others
must be dedicated to a program until task
completion. (e.g. printer) Security Few security
measures are required.
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Multi-user, multi-tasking O/S

• Definition O/S that allows one or more users to
  carry out one or more tasks at any one time.
• CPU, Memory Management similar to a
  single-user, multi-tasking O/S.
• I/O Normally supports a large number of devices
  e.g. terminals that each user can use to
  communicate with the O/S.

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Multi-user, multi-tasking O/S
Security Uses a variety of techniques Login
procedures Usernames / Passwords File Access
Rights Home directories Data sharing Multi-user
O/S uses File ownership File access
rights Email to allow users to share information
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Real-time O/S

• Definition O/S where the predictability of the
  speed of response and reliability are essential.
• Usually part of a feedback loop Responds to
  events so that it can influence those events.

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Real-time O/S

• Often found in embedded systems within process
  control.
• Can be single-user or multi-user.
• Normally multi-tasking.

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Real-time O/S
CPU, Memory, I/O, SecuritySimilar management of
these resources depending on whether single-user
or multi-user. Reliability Often incorporates
support for redundant components.e.g. multiple
hard disks and processors, for mission-critical
applications. Predictability A predictable
response time is essential in a real-time o/s.