Two kinds of software

• System software — manages the computer and hardware and provides a platform for other programs. Examples: the operating system, device drivers, utility programs and translators.
• Application software — lets the user do a specific task. Examples: word processor, spreadsheet, web browser, games, photo editor.

Rule of thumb: if it helps run the computer itself, it is system software; if it helps you do a job, it is application software.

System or application?

Tap a piece of software, then tap the group it belongs to.

The operating system (OS)

The operating system is the main system software. It manages the computer so users and applications can work without controlling the hardware directly. Its tasks include:

• Managing memory and running processes (multitasking).
• Managing input/output devices and their drivers.
• Managing files and the file system, and handling security (user accounts, passwords).
• Providing a user interface (e.g. a GUI) between the user and the hardware.

What does the OS do?

Utility programs

Utility software helps to maintain, configure and protect the computer. Common examples:

• Anti-virus / anti-malware — scans for and removes malicious software.
• Backup — makes copies of files so they can be restored if lost.
• Disk defragmenter — reorganises fragmented files on a magnetic disk so they are stored together, speeding up access.
• File / disk management and compression tools.

Which utility?

High-level vs low-level languages

• High-level language (e.g. Python) — close to human language, easier to write and understand, and portable across machines. Must be translated before the CPU can run it.
• Low-level language — close to the hardware. Assembly language uses short mnemonics (e.g. LDA, ADD); machine code is pure binary that the CPU runs directly. Fast and gives fine control, but hard for humans.

Key point: the CPU can only execute machine code. High-level and assembly programs must be translated into machine code first.

Translators

• Compiler — translates a whole high-level program into machine code in one go, producing an executable file. Errors are reported together at the end; runs fast once compiled.
• Interpreter — translates and runs high-level code one line at a time. Stops at the first error, which makes it good for developing and debugging, but it runs more slowly.
• Assembler — translates assembly language into machine code.

Match the translator to its job

Tap a description on the left, then its matching term on the right.

Compiler or interpreter?

What the CPU runs

System or application?

The big ideas to know

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