OSAT Computer Science (181)

An operating system (OS) is software that manages hardware resources and provides services for application programs. It acts as an intermediary between users and computer hardware.

Process management involves creating, scheduling, and terminating processes. The OS allocates CPU time to processes using scheduling algorithms such as:

Memory management allocates and deallocates memory space for programs. Virtual memory extends available memory by using disk space as an extension of RAM. Paging divides memory into fixed-size blocks; segmentation divides it based on logical program sections.

File system management organizes data storage through hierarchical directory structures. Common file systems include NTFS (Windows), APFS (macOS), and ext4 (Linux). The file system tracks file locations, permissions, and metadata.

Device management coordinates communication with hardware through device drivers. Drivers translate OS requests into device-specific commands.

Security management controls user authentication, authorization, and access control. The OS enforces permissions determining which users can access which resources.

Desktop operating systems (Windows, macOS, Linux distributions) provide graphical interfaces for personal computers. They support multitasking, multiple users, and a wide range of applications.

Server operating systems (Windows Server, Linux server distributions) optimize for network services, reliability, and security. They handle web hosting, file sharing, database management, and enterprise applications.

Mobile operating systems (Android, iOS) design for touchscreen interfaces, battery efficiency, and cellular connectivity. They emphasize app ecosystems and cloud integration.

Embedded operating systems run on specialized hardware like routers, appliances, and IoT devices. They prioritize small footprint, real-time responsiveness, and stability.

Real-time operating systems (RTOS) guarantee response within strict time constraints. They control industrial equipment, medical devices, and automotive systems where timing is critical.

Command-line interfaces (CLI) accept text commands typed by users. They provide powerful control and scripting capabilities but require memorizing command syntax.

Graphical user interfaces (GUI) present visual elements like windows, icons, menus, and buttons. They lower the learning curve but may limit advanced functionality.

Touch interfaces use gestures like tap, swipe, and pinch for mobile and touchscreen devices. Voice interfaces accept spoken commands and provide audio responses.

Application software helps users do specific tasks. The OS runs it and gives it access to files, memory, and devices.

Software is installed locally, run in a browser as a web app, or delivered as a cloud service (software as a service). Updates and patches fix bugs and close security holes.