Systems Software

Operating Systems

What you will know

Common features of an Operating System

HCI, File Management, error reporting, memory management

Modes of processingInteractive & Real-time

Device DriversTypes of filing system

Flat & Hierarchal

Types of accessRandom & 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 softwareProgram

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

Open word

processor

10110110

OS

Standard Functions of the OS

Controls input/outputThe 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

InteractiveAccepting 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 softwareCommon features of HLLTypes of language

Special PurposeGeneral Purpose

TranslatorsCompilerInterpreter

Systems Software

The operating system is just one example of systems software.Other examples of systems software are:

Anti-virus toolsDisk utilities Programming toolsPrinter 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

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” InterpreterProgram

HELLO

Current Location

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 programDifficult to detect errors

Compiler

CompilerProgram

Compiled Program (Machine Code)Source Code

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

Assembly Language Machine Code

LDA #28

PRN #76

CLE #1

JMP #8

011000011100

101001001100

100100000001

110100001000

Assembler