1. Systems Software
Operating Systems

2. 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

3. 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)

4. 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.
OS is a program like word but is a systems software
The Operating System is Systems Software

5. Operating Systems
The operating system (OS) is the most important program used by the computer.
The OS organises many things within the computer.

6. 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.

7. Examples of OS Windows Linux Mac OS
Unix for large file servers and networks

8. 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 OS

9. 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.

10. 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

11. 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.

12. 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.

13. 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.

14. 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.

15. 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)

16. Hierarchical filing system
Computer
C:/
D:/
Drives 
Folders  
Files

17. 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

18. Access Types Random/Direct Access Sequential 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

19. Systems Software

20. What you will know Other examples of systems software
Common features of HLL
Types of language
Special Purpose
General Purpose
Translators
Compiler
Interpreter

21. 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...

22. 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…

23. Types of Language General purpose Special 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.

24. Translators High Level languages need to be changed into machine code.
This is done using a translator
Types of translator:
Compiler
Interpreter
Assembler

25. Interpreter Translates line by line Immediately executes HLL programs
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

26. Interpreter Current Location 10 Print “HELLO” HELLO Interpreter
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
Interpreter
Program
10 Print “HELLO”
HELLO

27. 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

28. Compiled Program (Machine Code)
Compiler
Compiled Program (Machine Code)
Source Code
Compiler
Program

29. 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

30. Assembler Assembler 011000011100 LDA #28 101001001100 PRN #76
LDA #28
PRN #76
CLE #1
JMP #8
Assembler
Assembly Language
Machine Code