System softwara cs

Why do we need an Operating System?

Acts as an interface between the user and hardware, manages resources, and allows software to run efficiently and securely

Six main function categories of an OS

Resource management, file management, interrupt handling, security, user interface, and system utilities

OS memory management for multitasking

Allocates RAM to programs, schedules CPU time, and manages data transfer to and from storage

Interrupt Handling

OS process that pauses a running program to respond to urgent events such as hardware faults or user input

OS security features

User accounts and passwords, access permissions, firewalls, antivirus software, and file encryption

Memory Management

Allocates and deallocates RAM, enables multitasking, and prevents programs accessing each other’s memory

Paging vs Segmentation

Paging uses fixed-size blocks causing internal fragmentation, while segmentation uses variable-size blocks causing external fragmentation

Virtual Memory

Uses secondary storage as extra RAM, allowing more programs to run but with slower performance than physical RAM

Round Robin scheduling

Preemptive scheduling using time slices where processes cycle through a queue fairly without priority

First-Come-First-Served scheduling

Non-preemptive scheduling where processes run in arrival order, risking the convoy effect

Multi-Level Feedback Queue

Preemptive scheduling with multiple priority queues where long-running processes move to lower priorities

SJF vs SRTF

SJF is non-preemptive and selects the shortest job, while SRTF is preemptive and selects the shortest remaining time

BIOS

Firmware that performs POST and loads the operating system during boot

Device Driver

Software that allows the OS to communicate with hardware using device-specific instructions

Virtual Machine

Software emulation of a computer system allowing multiple operating systems to run on one physical machine

Application vs Utility Software

Application software performs user tasks, while utility software maintains and manages the system

Open Source vs Closed Source

Open source code is publicly available and modifiable, while closed source code is private

Types of Translators

Interpreters execute line by line, compilers translate whole programs, and assemblers convert assembly to machine code

Interpreter vs Compiler

Interpreters are slower but easier to debug, while compilers are faster and produce standalone executables

Stages of Compilation

Lexical analysis, syntax analysis, code generation, and optimisation

Static vs Dynamic Linking

Static linking combines libraries at compile time, while dynamic linking links libraries at runtime

Linker vs Loader

The linker creates the executable, while the loader loads it into RAM for execution