1. Systems Software & Operating systems

2. Computer Languages

3. Programming languages
All software is written in special programming languages.
The CPU of the computer can only understand it’s own language – zeros and ones.

4. Programming languages
Programming languages are broken down into:
Low Level Language
High Level Language

5. Low Level Language Machine Code
All instructions in every program must be translated into the computers own language called Machine Code
Machine Code uses commands that we do not necessarily understand as humans
It uses binary numbers to represent commands

6. Machine Code Example

7. Machine Code - Advantages:
Because this is the computers own language:-
programs do not need to be translated
therefore, programs run very fast

8. Machine Code - Disadvantages
Difficult for humans to program in Machine Code
Difficult to locate errors (DEBUG)

9. High Level Language
A computer language that uses commands similar to the English Language
True Basic
Comal
Pascal
Fortran
Prolog

10. Advantages: HLL Easier to read, understand and write programs
Easier to locate errors (Debug)

11. Portability:
A Program is portable if it can run on different Operating Systems or Platforms

12. Disadvantages: HLL
Instructions written in a HLL must be TRANSLATED into machine code before the CPU understands the instruction
This takes time making the program slower to run

13. Translator Programs
Programs which will translate the instructions of a program into Machine code.
There are 2 types of translator:
Interpreter
Compiler

14. Source and Object Code
Source code is the list of instructions written in a High Level Language
Object Code is the translated version of the instructions written in Machine Code

15. Interpreter
Translates the instructions of a program written in a HLL into Machine code one instruction at a time.
LET TOTAL = 0
FOR COUNTER = 1 TO
PRINT “PLEASE ENTER NUMBER”
INPUT NUMBER
LET TOTAL = TOTAL+NUMBER
NEXT COUNTER
PRINT “THE TOTAL IS “;TOTAL
END

16. Note: Interpreter Easier to learn to program as errors
are identified as commands are entered
Changes are made easily
Runs slower
Must have the interpreter loaded into memory for the program to run (requires more memory).
Does not produce Object Code

17. Compiler
Translates the instructions of a program written in a HLL into Machine code in a single operation.
LET TOTAL =
FOR COUNTER = 1 TO
PRINT “PLEASE ENTER NUMBER”
INPUT NUMBER
LET TOTAL = TOTAL+NUMBER
NEXT COUNTER
PRINT “THE TOTAL IS “;TOTAL
END
SOURCE CODE
OBJECT CODE

18. Note: Compiler Changes are not easily made. Runs fast
The original source code will have to be edited and translated again
Runs fast
Produces Object Code which can be run without the compiler being present in memory - efficient

19. Now do Homework sheet 1 on Systems Software
Classwork Questions
Why do HLL's need translation?
How do translators help programmers?
State two common features of all HLL's.
Name two types of translator.
Describe how an interpreter works
Describe how a compiler works.
What are object and source code?
If someone were just learning how to write programs, which type of translator would you recommend they use?          (Give two reasons to justify your answer)
By considering a compiler and interpreter, which type is more efficient?  (Give two reasons to justify your answer)
Now do Homework sheet 1 on Systems Software

20. Revision - Types of Files
Program files - software is another name for a program file
Program files are made up of instructions which the computer follows (Microsoft Office, Windows XP)

21. Revision - Types of Files
Data files - The files you create using the software on the computer
These are files containing data which a computer user has created (Personal Profile, Dental Check up Database, Olympic Pentathlon Spreadsheet)

22. Software A computer cannot work without software
All the jobs that a computer can do are controlled by a program
Different computers can have different software installed but all computers must have:-

23. An Operating System
The Operating System is the set of programs which controls the entire operation of the computer and any devices that are attached to it
The OS runs from the minute the computer is switched on until it is switched off

24. Types of Operating System
Windows XP 98 95
MAC OS

25. Functions of the Operating System
Memory Management
File Management
Error Reporting
Human Computer Interface

26. Memory Management
This program in the Operating System controls where data and programs are placed in Main Memory

27. File Management
This program in the Operating System deals with storing and retrieving files from backing store

28. Error Reporting
This program in the Operating System deals with Letting the user know if any mistakes have occurred

29. Human Computer Interface
This program in the Operating System provides a human computer interface for the user

30. ROM and RAM The OS can be stored in ROM or RAM.
If stored on ROM chip the chip must be removed to update the OS
If stored in RAM it can be updated quickly and easily by overwriting with the new version of the OS

31. Directory / Folder
This is an area on backing storage where files are stored

32. Filing system

33. Filing Systems There are 2 main types of filing system Flat
Hierarchical

34. Flat Filing System
This system presents all file information in one level
1 Text File Spreadsheet File 1
2 Excel File Text File 2
3 Word Processing File Database SS
4 Word Processing File Spreadsheet File 2

35. Flat (Disadvantages) Not user friendly Poorly organised
Difficult to find files if the user forgets the name of it
Groups of files can’t be protected from unauthorised users
All files might not be able to be seen on the monitor screen

36. Hierarchical Filing System
This system allows different levels to be set up and presented
Files can be grouped together
Files are organised into
Directories
Sub-directories

37. Root Directory
Text File 1
Text File 2
WP File 1
WP File 2
SS File 2
SS File 1
ClarisWorks SS
ClarisWorks WP
HARD DISK
PROGRAM FILES
DATA FILES
TEXT FILES
SS FILES
WP FILES
Sub-directories

38. Hierarchical (Advantages)
More user friendly
Better organisation
Files can have the same names provided they are not in the same directory
Directories can be protected from unauthorised users
Easier to find files (Is this a good thing?)

39. Sequential Access to Data
The data has to be accessed in the order it is stored. Access is slow

40. Random Access to Data
The data has to be accessed in the any order. Access is fast as we can go directly to the data required.

41. Interactive Systems
In an Interactive System the user and the computer communicate, they interact, and the computer program responds directly to commands

42. Interactive systems

43. Real-Time system
A Real-time system is an interactive system which cannot afford to have a delay in the time taken for the computer to respond.
Response in a Real-time system is vital

44. Background Job Capability
This is when the operating system carries out a task in the foreground and another task in the background. The processor is so quick the user thinks that the tasks are happening at the same time

45. Background Job Capability
Example
The computer can print a document as a background task while at the same time appear to allow the user to word process a document as a foreground task. The user does not have to wait on the print job finishing before continuing to word process a document.

46. Device Drivers Scanner
A device driver is a program which is an add-on to the operating system in a computer, to allow the computer to operate a particular device which is attached to it
Scanner

47. Printer Drivers
A Printer driver is a program which is an add-on to the operating system in a computer, to allow the computer to operate a particular printer which is attached to it

48. Now do Homework sheet 2 on Systems Software
Classwork Questions 2
Files can be stored on disc on a Flat filing system or a Hierarchical filing system. Describe each system. (A diagram may be helpful in your answer)
Which type of filing system do you use for storing your computer files and why?
Draw a hierarchical representation of how you store your files on your computer system.
What is the purpose of system software?
Name two examples of system software.
Why might an operating system be thought of as the most important piece of software a computer uses?
Name the four functions of an OS.
Describe four functions of an OS
Now do Homework sheet 2 on Systems Software

49. End of Unit Check Up
You can now try the Interactive Revision exercise for this unit.