Systems Software & Operating systems

Computer Languages

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.

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

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

Machine Code Example 111111111111111111111111 000000000000000000000000 101010101010101010101010 010101010101010101010101

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

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

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

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

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

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

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

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

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 10 00000111101010000110101011 PRINT “PLEASE ENTER NUMBER” INPUT NUMBER LET TOTAL = TOTAL+NUMBER NEXT COUNTER PRINT “THE TOTAL IS “;TOTAL END

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

Compiler Translates the instructions of a program written in a HLL into Machine code in a single operation. LET TOTAL = 0 000001111010100001101010111 FOR COUNTER = 1 TO 10 101010101010101010101010101 PRINT “PLEASE ENTER NUMBER” 000111000111000111001110010 INPUT NUMBER 111111111111111111111000000 LET TOTAL = TOTAL+NUMBER 111111110000000000000000000 NEXT COUNTER 111111111111000000000011111 PRINT “THE TOTAL IS “;TOTAL 000000000011111111100000001 END 111100001110001110001110001 SOURCE CODE OBJECT CODE

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

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

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)

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)

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:-

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

Types of Operating System Windows XP 98 95 MAC OS

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

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

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

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

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

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

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

Filing system

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

Flat Filing System This system presents all file information in one level 1 Text File 1 5 Spreadsheet File 1 2 Excel File 1 6 Text File 2 3 Word Processing File 1 7 Database SS 4 Word Processing File 2 8 Spreadsheet File 2

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

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

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

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?)

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

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.

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

Interactive systems

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

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

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.

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

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

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

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