2. Functionality

Emulator

Software that lets one computer pretend to be a completely different one, like running a Windows environment inside a Mac.

Cross-platform application

An app designed to run smoothly on multiple completely different operating systems (like working on Windows, Mac, and Linux).

Multiprogramming

When an OS loads several programs into the main memory at the exact same time so the CPU always has a task ready to work on.

Multitasking

The ability of an OS to run multiple apps and processes at the same time by quickly sharing the CPU's attention and memory between them.

Preemptive Multitasking

A modern method where the OS takes total control, forcing the CPU to split its processing time equally among all open apps.

Cooperative Multitasking

An old method where an app takes control of the CPU and won't let go until it is completely finished or chooses to hand it back.

Hybrid Multitasking

A mix of both styles: the OS will forcefully interrupt a process if needed, but apps can also voluntarily give up the CPU.

Multithreading

Breaking down a single program into smaller pieces (threads) so the CPU can run multiple parts of that same program at the same time.

Concurrency

The ability of different parts of a program or multiple threads to safely look at and use shared data at the exact same time.

Batch processing

Grouping a huge pile of repetitive data tasks together and running them all at once automatically (like processing payroll overnight).

HCL (Hardware Compatibility List)

An official checklist of computer parts and gear that are guaranteed to work with a specific operating system.

Process Control System Calls

Commands that tell the OS to start, stop, or manage active programs.

File Management System Calls

Commands used to create, delete, read, write, or organize files on a drive.

Device Management System Calls

Commands that help the software talk directly to hardware pieces like printers, screens, or keyboards.

Information Maintenance System Calls

Commands used to check or change background details like the system time, date, or file details.

Communication System Calls

Commands that open connections and send messages between different programs or across a network.

Protection System Calls

Commands that control permissions, deciding which users or programs are allowed to open specific files.

Operating system life cycle

The entire timeline of an OS, starting from its public release all the way until the creators stop supporting it.

End-of-life (EOL)

The exact date when an OS completely stops receiving updates, fixes, or support from its creators.

Extended Support

A final safety stage where an older OS stops getting new features or normal bug fixes, and only gets critical security patches.

Process Control Block (PCB)

A tiny tracking sheet the OS uses to remember everything about a running app, like its current progress and memory use.