Outcome 1:
Describe the structure and function of
an operating system.
Systems Software
Computer
System
Hardware
Software
Systems
Applications
Software
Software
Examples of Software types
Applications Software:
Word Processor, Spreadsheet,
Database, Desktop Publishing
Systems Software:
Compilers, Interpreters
System utilities
Operating systems
Operating Systems
An operating system is a collection of
system programs that together control,
manage and monitor the operation of a
computer system.
Examples:
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Controls the execution of applications software
Controls the operation of the hardware
Monitors the use of the hardware
Provides a user-interface
Operating System
Operating
System
Hardware
Applications
Software
User
An operating system can be regarded as providing
a layer between the user, applications and the
underlying hardware.
Types of Operating Systems
o
General Purpose
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o
Used in computers.
Provide the ability to run a number of
different applications.
Examples: all versions of Windows
Embedded Systems
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Do not manage user programs at all
Perform a well-defined task, usually in a realtime environment
Used to control hardware devices such as
cars, electronic appliances etc.
Examples: DVD players, car fuel injection etc.
Types of Operating Systems
Types of Operating Systems
Single-user
Single-tasking
Multi-user
Multi-tasking
Multi-tasking
Real-time
Types of Operating Systems
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Single-user, single-tasking
Example: MS-DOS
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Single-user, multi-tasking
Example: Windows XP
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Multi-user, multi-tasking
Example: Linux
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Real-time
Example: OSE, QNX
Functional Areas of an OS.
User Interface
File Management
Input Output
Memory Management
Kernel
The Kernel
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Part of the O/S that is responsible for
process management, multi-tasking and
interrupt handling.
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Loads and runs other parts of the o/s when
required.
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Must reside permanently in memory during
computer operation.
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
The Boot Process
The core of an OS (known as the kernel)
must be present in main memory.
At power-on,
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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.
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.
Storage of the Operating System
Storage of an O/S in a computer system may
be either on
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ROM chip
Or
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Hard Disk
ROM based O/S
The operating system is held on a ROM chip.
The ROM is configured as part of the main
memory.
Advantages:
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The O/S is immediately in control at power up.
Cannot be corrupted
Disadvantage
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Updates to O/S require replacement of ROM chip
Most usually found in embedded systems.
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:
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The O/S is easily updated
No limit to the size of the O/S
Disadvantages:
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The O/S is easily corrupted
Loading of the O/S may take a considerable time.
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)
Single-user, single-tasking O/S
I/O:
The currently running program is
given full dedicated access to all
I/O devices.
Security: Very few security measures are
required.
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.
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.
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 singleuser, 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.
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
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.
Real-time O/S
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Often found in embedded systems
within process control.
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Can be single-user or multi-user.
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Normally multi-tasking.
Real-time O/S
CPU, Memory, I/O, Security:
Similar management of these
resources depending on
whether single-user or multiuser.
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.