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Systems Software
Operating Systems
What you will know
Common features of an Operating
System
HCI, File Management, error reporting,
memory management
Modes of processing
Interactive & Real-time
Device Drivers
Types of filing system
Flat & Hierarchal
Types of access
Random & Sequential
What is software?
Software is the term that we use for all the
programs and data that we use with a
computer system.
Two types of software
Program
The instructions that the computer follows
(e.g. a word processor or a game).
Data
What the programs process (e.g. a word
processing document or a saved game)
More on software
There are two types of program software.
Applications software
Programs designed to carry out a manual task
(Word Processors, Databases, Graphics etc.)
Systems Software
Programs used to organise the computer,
handle its devices, manage memory etc.
The Operating System is Systems Software
Operating Systems
The operating system (OS) is the most
important program used by the computer.
The OS organises many things within the
computer.
Operating Systems (OS)
The OS is stored on hard disc and loaded into
RAM when the computer starts up.
Some computers store their OS in ROM so that
it cannot be erased by accident.
The operating system controls and monitors
the operation of the computer system.
The filing system is part of the OS and it
controls the loading and saving of programs
and data from backing storage.
Examples of OS
Windows
Linux
Mac OS
Unix for large file servers and networks
Standard Functions of the
OS
User interface (HCI)
The OS provides the means of the user
communicating (interacting) with the
computer system
Features such as windows, icons, menus,
commands, etc. are all provided by the
operating system
1011
0110
Open
word
processor
OS
Standard Functions of the
OS
Controls input/output
The access to all devices attached to the
computer is controlled by the OS.
For example, the OS can stop two programs
trying to use the same device at the same
time.
Standard Functions of the
OS
Manages memory
Controls where programs and data are
placed in the main memory.
Error Reporting
The operating system lets the user know if
any mistakes have occurred
E.g. No paper in printer
Modes of Processing
Interactive
Accepting input from a human.
Interactive computer systems are programs
that allow users to enter data or commands.
Most popular programs, such as word
processors and spreadsheet applications, are
interactive.
In interactive processing, the application
responds to commands as quickly as it can
once they have been entered.
Sometimes there is a delay while the processor
finishes another task.
Modes of Processing
Real-Time
Real-time operating systems are systems
that respond to input immediately.
Automatic teller machines for banks are an
example of real-time processing.
Real-time systems are used for tasks such
as navigation, in which the computer must
react to a steady flow of new information
without interruption.
Interactive Systems with
Background Job Capability
Some operating systems allow a background
process to occur at the same time as a
foreground interactive process.
The foreground process is the one that accepts
input from the keyboard, mouse, or other input
device.
Background processes cannot accept interactive
input from a user.
For example, some word processors
print files in the background,
enabling you to continue editing
while files are being printed.
Device Drivers
A device driver is a program which is an
add-on to the operating system in a
computer
It is used to allow communication
between a particular device and the
computer.
A scanner or a printer are examples of
devices that may need drivers.
Filing System
The filing system manages backing
storage
It controls access to all types of backing
storage devices
It will prevent two programs trying to
access the same files at the same time.
Data stored in backing storage
in areas called Directories
(Windows call them folders)
Hierarchical filing system
Computer
C:/
D:/
Drives
Folders
Files
Hierarchical filing system
A filing system in which directories have files
and subdirectories beneath them.
A hierarchical filing system is one that uses
directories to organise files into a tree structure.
Work on same topic can be grouped together
Easier to find files as they are in their own
directory
Files can have the same name as long as in
different directories
Access Types
Random/Direct Access
Retrieves the data you want
straight away.
CD-ROM drive, Hard disc drive,
Floppy disc drive.
Sequential Access
Move through record after
record to find the data you want.
Magnetic tape
Systems Software
What you will know
Other examples of systems software
Common features of HLL
Types of language
Special Purpose
General Purpose
Translators
Compiler
Interpreter
Systems Software
The operating system is just one example
of systems software.
Other examples of systems software are:
Anti-virus tools
Disk utilities
Programming tools
Printer manager utilities
All these are examples of programs.
Programs can be written in a number of
different ways...
High Level Languages
Common Features
Written similar to English
Common internal structures
loops, IF & Case statements
Built in error checking
Portable (can be moved to different
machines)
Most designed for special purpose…
Types of Language
General purpose
Written for a wide variety of tasks.
They can be used for any type of application
however may make particular tasks difficult
to do.
Special Purpose
Special purpose high level languages are
written for particular types of task.
For example: Basic, Pascal, C, etc
Make tasks easier to carry out.
Translators
High Level languages need to be
changed into machine code.
This is done using a translator
Types of translator:
Compiler
Interpreter
Assembler
Interpreter
Translates line by line
Each HLL statement is translated, converted
and turned in to machine code.
Immediately executes HLL programs
Is used during build and testing.
Needs to be translated every time program
is executed
Interpreter
Current Location
10 Print “HELLO”
20 Print names$
30 LET a=a+1
40 Repeat
50 a=a+1
60 b=b+2
70 UNTIL Not d+23=1
80 “Screenload “file1”
90 Execute code2
10 Print “HELLO”
Interpreter
Program
HELLO
Compiler
A program that translates source code
(HLL) into machine code in one go.
Final program only translated once.
Compiled program runs faster then
interpreted one.
Other machines don’t need translator to
execute program.
Takes time to produce program
Difficult to detect errors
Compiler
Compiled Program
(Machine Code)
Source Code
Compiler
Program
Assembler
Assembly language has the same structure
and set of commands as machine code, but
it allows a programmer to use names instead
of numbers.
Uses less memory than HLL
Program execution fast compared to HLL
Written for one type of processor won't run
on another.
Harder to program
Assembler
LDA #28
011000011100
PRN #76
101001001100
CLE #1
Assembler
JMP #8
Assembly Language
100100000001
110100001000
Machine Code