Software

📌 Key points

1. System software manages the computer and provides a platform for other programs, e.g. the operating system and utility software (anti-virus, defragmentation, backup, compression); application software lets the user carry out tasks, e.g. a word processor, spreadsheet or web browser.
2. Functions of an operating system: managing files, handling interrupts, providing a user interface, managing peripherals and drivers, managing memory, managing multitasking, providing a platform to run applications, providing security and managing user accounts.
3. Software is layered: the hardware runs firmware (e.g. the bootloader stored in ROM), the firmware loads the operating system, and applications run on the operating system.
4. An interrupt is a signal from a hardware device (e.g. a key press, printer out of paper) or software (e.g. division by zero) asking for the CPU's attention; the current task is paused, an interrupt service routine handles it, then the task resumes.
5. High-level languages are close to English, easier to read, write and debug, and portable between different computers; one statement becomes many machine code instructions.
6. Low-level languages are machine code (binary) and assembly language (mnemonics such as LDA, ADD); they are specific to one type of CPU but give direct control of hardware and can be very efficient. Assembly language is translated by an assembler.
7. A compiler translates the whole program in one go into an executable file; errors are reported after translation, the program then runs without the compiler, and the source code does not need to be shared.
8. An interpreter translates and runs the program one line at a time and stops at the first error, which helps debugging during development; the interpreter is needed every time the program runs.
9. An IDE (integrated development environment) provides a code editor, a run-time environment, a translator, error diagnostics, auto-completion, auto-correction and prettyprint (colour-coding and indenting code).

📖 Key terms

Operating system

System software that manages the hardware and resources and provides a platform for applications.

Utility software

System software that maintains or protects the computer, e.g. anti-virus or defragmentation.

Firmware

Software stored permanently in ROM that controls hardware, such as the bootloader.

Interrupt

A signal sent to the CPU from hardware or software to say that something needs attention.

Compiler

Translates a whole high-level program into machine code at once, producing an executable file.

Interpreter

Translates and executes a high-level program one line at a time.

Assembler

Translates assembly language into machine code.