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Scheme of work – Cambridge IGCSE® Computer Studies (US) 0441
Unit 10: Operating systems
Recommended prior knowledge
In order to understand the role of an operating system, students should have had practical experience of using at least one operating system with a GUI.
Context
Students should study this unit before starting Unit 11. For this unit, as well as Units 9 and 11, Computer Studies Support Booklet – Part 5
(http://teachers.cie.org.uk/docs/dynamic/31800.pdf) provides notes on section 5 of the syllabus and practice problems (with answers in Computer Studies Support
Booklet – Answers (http://teachers.cie.org.uk/docs/dynamic/31801.pdf).
Outline
The nature of batch, online, multi-access, real-time transaction processing, multitasking, network and process-control operating systems. Types of interface between
the operating system and the user. How folders are structured and how folders and files can be managed. Peripheral control, including the use of buffers, interrupts
and priorities, polling, handshaking and checksums.
Syllabus
ref
Learning
objectives
5.2.1
Introduction
Suggested teaching activities
Learning resources
Introduce:
• the idea of system software as different from applications software
• general tasks and facilities of an operating system – for processor
management, it is helpful to demonstrate Windows Task Manager
• role of the operating system (OS) in file management
• the idea that microprocessors or microcontrollers in automated devices
such as refrigerators and microwave ovens do not require an
operating system since they only execute a single program.
LWS coursebook pp. 92–4
www.igcseict.info/theory/1/os/
Introduction to operating systems
www.howstuffworks.com/operating-system1.htm
First of two pages describing operating systems and their
functions
www.howstuffworks.com/operating-system4.htm
Description of the loading of an operating system
www.howstuffworks.com/operating-system5.htm
First of two pages describing processor management and
the use of the Process Control Block (PCB), a data
structure containing the information needed to manage a
particular process, in multi-tasking
v1 2Y05
Cambridge IGCSE Computer Studies (US) 0441
1
Syllabus
ref
Learning
objectives
The nature of
batch, multiaccess, real-time
transaction
processing,
multitasking,
network and
process control
operating systems
5.2.2
5.2.3
v1 2Y05
The form of
interface between
the operating
system and the
user; use of
command line
and use of
graphical user
interfaces
Management of
files; file
directories;
Suggested teaching activities
Introduce the different types of processing system taking care to ensure
that students understand the differences between them, especially the
difference between the sorts of operating system required to support
application programs for real-time transaction processing and real-time
process control
Note that:
• real-time processing involves processing input within a guaranteed
maximum time
• a real-time transaction processing system is an online system that
processes individual, whole transactions as they occur, e.g. an airline
booking system or automated stock control system, where the
maximum response time needs to be in the range of seconds –
nowadays users tend not to tolerate delays of tens of seconds or even
whole minutes
• this use of the term real-time differs from its use in a real-time
process control system, which continuously monitors and processes
sensor data sufficiently rapidly to produce the output required to keep
pace with the user’s needs for information or control – although control
of a greenhouse would probably tolerate a delay of a few seconds or
even a few minutes, in most cases, this means a maximum response
time between microseconds and seconds.
Review students’ previous experience of operating systems with graphical
user interfaces (GUI), perhaps in Unit 7, and introduce the idea of a
command line interface.
Discuss the main differences between command line interfaces and GUIs
and their respective advantages and disadvantages.
Explain that:
• a file directory is an index of the contents of a virtual container for files
and sub-directories maintained by the operating system’s file manager
Cambridge IGCSE Computer Studies (US) 0441
Learning resources
www.howstuffworks.com/operating-system7.htm
First of two pages describing memory and device
management
LWS coursebook pp. 94–8
www.howstuffworks.com/operating-system3.htm
Description of different types of operating system
www.teachict.com/gcse_computing/ocr/213_software/os_types/miniw
eb/pg4.htm
Notes on network operating systems
LWS coursebook pp. 98–101
www.igcseict.info/theory/1/uis/index.html
Types of user interface
www.teachict.com/gcse_computing/ocr/213_software/user_interface/
home_user_interface.htm
Theory notes, activities and quizzes on user interfaces
LWS coursebook pp. 101–2
2
Syllabus
ref
5.2.4
v1 2Y05
Learning
objectives
Suggested teaching activities
folders
•
Peripheral device
control; use of
buffers; interrupts
and interrupt
priorities; polling;
handshaking;
checksums
Learning resources
in a GUI, a directory is displayed as a folder and the two terms are
often used interchangeably.
Students need to perform practical exercises to ensure that they
understand the need for and use of facilities to copy, move, list and print
files and create sub-directories.
Introduce the ideas that:
• peripheral devices such as keyboards and printers must be controlled
and responded to by the operating system
• communication between the computer and peripherals must be
controlled and errors detected.
Explain that:
• a buffer is an area of memory used to hold data temporarily to
compensate for different rates of processing data by the processor
and a (slower) peripheral and allow the processor to perform other
tasks while waiting to receive or send data
• in order to respond to messages from peripheral devices, the
processor can use one of two methods:
• polling – the OS is responsible for periodically interrogating each
peripheral device in turn to discover its status, or
• interrupts – the OS is free to process other tasks until a
peripheral device sends an interrupt signal, indicating that it needs
the OS’s attention
• handshaking involves sending electronic signals during transfer of
data to control the flow of data between the computer and a peripheral
device (or over a network with another computer) to prevent a delay in
processing data at the receiving end resulting in lost data
• since a block of data (such as a USB packet) may be corrupted during
transfer, a checksum can be:
• used to summarise the block before transmission by calculating
the arithmetical sum of the numerical values of all its elements
and
• transmitted with the block to provide a check after transmission
(similar to a check digit used to validate a much shorter numerical
ID code).
Cambridge IGCSE Computer Studies (US) 0441
LWS coursebook pp. 102–5
www.teachict.com/gcse_new/computer%20systems/buffers_drivers/h
ome_buffers.htm
Theory notes and activities on buffers (and drivers)
www.atarimagazines.com/compute/issue149/60_Interrupt
s_made_easy.php
Article that compares interrupts with polling
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