Software: Class 9 Computer Science

Key points

Software is a set of instructions, called a program, that tells the computer what to do. It cannot be touched. Without software the hardware would be useless. Software is mainly of two kinds: system software and application software.

System software controls and manages the computer hardware and provides a base on which other programs can run. The main kinds are the operating system, utility programs and language translators. It usually starts working when the computer is switched on.

An operating system (OS) is the main system software. It acts as a link between the user and the hardware. Examples are Windows, Linux, macOS, Android and iOS. Its main functions are:

• Process management: decides which program uses the CPU and when.
• Memory management: gives RAM to programs and takes it back when they finish.
• File management: creates, names, stores, copies and deletes files and folders.
• Device management: controls input, output and storage devices through drivers.
• Security: protects the system with user accounts and passwords.
• User interface: lets the user communicate with the computer.

There are three common types of user interface:

• Command line interface (CLI): the user types text commands. It needs the commands to be remembered.
• Graphical user interface (GUI): uses windows, icons, menus and a pointer, so it is easy to use. Windows is an example.
• Touch or voice interface: used on phones and tablets.

Operating systems can also be grouped by how many users and tasks they handle:

• Single user, single task: one user runs one program at a time.
• Single user, multitasking: one user runs several programs together, as on a normal PC.
• Multi-user: many users share one computer at the same time.
• Real time: responds within a fixed small time, as in a traffic control or medical machine.

Language translators change a program written by a programmer into machine code, which is the only language the CPU understands:

• Assembler: converts assembly language into machine code.
• Compiler: translates the whole program at once and then runs it. It reports all errors together.
• Interpreter: translates and runs the program one line at a time and stops at the first error.

Utility programs perform maintenance tasks. Common examples are:

• Antivirus: finds and removes viruses and malware.
• Disk cleanup: deletes temporary and unwanted files.
• Backup: makes copies of data for safety.
• File compression: reduces file size, for example ZIP.
• Disk defragmenter: rearranges scattered file parts on a hard disk.

A device driver is a small program that lets the operating system communicate with a hardware device such as a printer or a graphics card. Without the right driver, the device may not work.

Application software is designed to help the user do a particular job. It is of two types:

• General purpose software: can be used for many tasks. Examples are word processors (MS Word), spreadsheets (MS Excel), presentation programs (PowerPoint), database software (Access), web browsers and graphics software.
• Special purpose software: made for one specific task. Examples are payroll systems, hospital management systems, library software and railway reservation systems.

Custom software is made to the exact needs of one organisation. Packaged (off-the-shelf) software is made for many users and sold ready to use. Custom software costs more but fits the needs better. Packaged software is cheaper and available at once.

Software can also be grouped by licence:

• Commercial software: must be bought, such as Microsoft Office.
• Shareware: free to try for a limited time, then must be bought.
• Freeware: free to use but the source code is not shared.
• Open source software: free, and the source code can be seen and changed, such as Linux and LibreOffice.
• Pirated software: illegal copies, which is a crime and may carry viruses.

Firmware is software stored permanently in ROM or flash memory inside a device, for example the BIOS that starts a computer or the program inside a washing machine. Software should be updated regularly to fix errors and security weaknesses.

Study tip: Make a tree diagram in your notes: Software splits into system and application, and each splits further with examples. Most questions ask for a definition, a difference or a list of functions, so practise stating each in one or two lines and always add a real example such as Windows, Linux, Excel or an antivirus.

Definitions and flashcards

Say the meaning first, then open the card to check.

Short questions with model answers

These are the kind of questions asked for 2, 3 and 5 marks. Try each one before opening the answer.

Common mistakes

• Writing that Windows or Linux is application software. They are operating systems, which are system software.
• Confusing a compiler with an interpreter. The compiler works on the whole program, the interpreter works line by line.
• Treating freeware and open source as the same. Freeware is free to use, but only open source gives access to the source code.
• Listing MS Word as system software. It is general purpose application software.
• Forgetting examples. A definition without an example often loses a mark.

Practise this chapter

Practice questions and timed test Printable worksheet