Types of Software & Interrupts

• Software splits into two families: system software (keeps the computer running) and application software (lets the user do a specific job).
• The operating system is the most important piece of system software — it manages hardware and gives applications a platform to run on, across 8 key functions.
• Utility software maintains, enhances, or repairs the system (e.g. defragmentation, compression, encryption, task manager).
• Communication flows in one direction through layers: application software → OS → hardware, never straight from app to hardware.
• Firmware (the BIOS/bootloader) lives permanently in ROM and gets the hardware ready before the OS even loads.
• An interrupt is a signal that forces the CPU to pause its current task and deal with something more urgent — the register contents get saved to a stack first so nothing is lost.
• Interrupts can come from hardware (key press, mouse click, power button) or software (a crash, division by zero, memory conflict).

Think of a computer like a restaurant. System software is everything behind the scenes that makes the restaurant able to function at all — the kitchen, the electricity, the staff rota. Application software is the actual menu items the customer orders — what they came in for.

System Software

System software is essential for the operation of the computer system — without it, nothing else can run. It gives the user a platform to run applications and carry out tasks. It includes:

• The operating system (covered in full detail below)
• Utility software — smaller programs that keep the system healthy

Utility Software — the "maintenance crew"

Utility software is designed to maintain, enhance, or troubleshoot/repair a computer system. Each utility does one specific, limited job — unlike the OS, which does everything at once. Here are the four you must know, grouped by what they actually achieve:

operating system (OS)

hides the complexity of the hardware