How operating systems work
The operating system (OS) is the main program that runs the computer. It starts first and stays on until you shut down. Its main jobs are:
- Process management: it decides which running program uses the processor and for how long, so many apps seem to run together.
- Memory management: it gives each app its own part of memory and takes it back when the app closes.
- File management: it keeps files in folders on the storage device.
- Device management: drivers let it control keyboard, screen, printer and network.
- User interface: windows, icons and touch, so that you can use the computer.
Examples: Windows, macOS, Linux, Android, iOS.
How application software works
Application software (an app) helps you do a task: writing, drawing, chatting, paying, learning. An app is a set of instructions written by programmers. When you open it, the OS copies it into memory and lets the processor run it.
An app uses system calls, which are polite requests to the OS: "open this file", "draw this window", "send this data". Because every app asks the OS in the same way, the same app can run on many different machines with the same OS.
Apps may be installed on the device or run in a web browser.
Software-based security technology
Software can also protect the computer:
- Antivirus scans files and removes malware (harmful programs).
- Firewall checks data entering or leaving a network and blocks suspicious traffic.
- Updates (patches) fix weak points that attackers use.
- Authentication: passwords, one-time codes and fingerprints prove who you are.
- Encryption scrambles data so that thieves cannot read it.
- Permissions: the OS lets each app use only what you allow, such as camera or location.
Software making up information systems
An information system uses several kinds of software together:
- System software (OS, drivers) that runs the machines.
- Database software that stores and finds shared data.
- Application software for tasks like billing, bookings or marks.
- Network and security software that connect and protect everything.
In a school, a marks app, a fee app and an attendance app can all use one student database. People enter and read the data, and the OS and servers keep it running.
Key formulas and definitions
- Layers: Hardware < Operating system < Apps < User
- OS jobs: process, memory, file, device, user interface
- App -> system call -> OS -> hardware -> answer back
- Security software: antivirus, firewall, updates, authentication, encryption
- Information system = apps + data + hardware + network + people
Worked examples
1. You open a music app and press play. Describe what the OS does.
The OS loads the app into memory, gives it processor time, finds the music file in storage, and sends the sound to the speaker through its driver. The app only asks; the OS does the work with the hardware.
2. Why is it risky to skip software updates?
Updates fix weak points that attackers already know. If you skip them, malware can use those weak points to get in. Updating closes the door.
3. A clinic uses a booking app, a billing app and a records app. Why should they share one database?
A shared database keeps one correct copy of each patient's data. The three apps then show the same facts, avoid repeated typing and do not disagree with each other.
Common mistakes
- Saying apps run directly on hardware. They run on the OS.
- Mixing up the OS and an app. The OS runs the machine; an app helps you with a task.
- Thinking antivirus alone is enough. You also need updates, passwords and care.
- Forgetting people and data in an information system. Software alone is not the whole system.