Operating System: Processes and Memory

• An operating system (OS) is software that manages computer hardware and software resources.
• It provides common services for computer programs.
• It acts as an intermediary between applications and computer hardware.
• The OS coordinates all activities on a computer.
• The OS allows you to interact with the machine.

Process Management

• A process is a program in execution.
• The OS manages the creation, scheduling, and termination of processes.
• When you open Microsoft Word, the OS creates a process and allocates memory and CPU time to it, managing its execution.

Memory Management

• The OS handles allocation and deallocation of memory space to programs as needed.
• Virtual Memory uses disk space to extend RAM.
• When you run multiple heavy applications simultaneously, the OS might move less-used data to the hard disk (swap space) to free up RAM for active programs.
• Paging divides memory into fixed-size blocks called pages.
• A 16MB program might be divided into 4KB pages, allowing the OS to load only needed pages into physical memory.

File Systems

• File Systems organizes and stores data on storage devices in a hierarchical structure.
• Windows uses NTFS or FAT32 file systems.
• Linux often uses ext4.
• These systems organize documents, photos, and other files in folders and subfolders.

Device Management

• Manages device communication through drivers.
• When you plug in a printer, the OS loads the appropriate driver to communicate with it and make it available to applications.

Process Scheduling

• Determines which processes run when and for how long to maximize CPU utilization.
• First-Come, First-Served (FCFS): Processes run in the order they arrive.
• Round Robin: Each process gets a small time slice in rotation.
• Priority Scheduling: Higher priority processes run first.
• While you're typing a document (low CPU usage), the OS may give background virus scanning lower priority, but when you start video rendering (intensive task), it gets higher priority.

Concurrency and Deadlocks

• Concurrency: Managing multiple processes executing simultaneously.
• An example of concurrency is playing music while browsing the web and downloading files.
• Deadlock: A situation where two or more processes are unable to proceed because each is waiting for resources held by the others.
• Process A holds Resource 1 and waits for Resource 2, while Process B holds Resource 2 and waits for Resource 1, is an example of deadlock.

User Interface

• Command-Line Interface (CLI): Text-based interface where users type commands.
• Windows Command Prompt and Linux Terminal, are examples of CLI.
• Graphical User Interface (GUI): Visual interface with windows, icons, and menus.
• Windows Desktop, macOS, and Ubuntu Desktop are examples of GUI.

Protection and Security

• Implemented via mechanisms to control access to system resources.
• User accounts, permissions, and authentication control who can access which files and perform which actions.

Practice Questions

• Database Management is NOT a function of an operating system.
• Thrashing involves excessive page swapping.
• Priority Scheduling might lead to starvation.
• A semaphore is a synchronization tool.
• The kernel is the core part of an operating system.
• The purpose of virtual memory is to allow execution of programs larger than physical memory
• A deadlock condition occurs when a process waits indefinitely.
• The "fork()" system call creates a new process in UNIX/Linux.
• A daemon in UNIX/Linux systems is a background process.
• VxWorks is an example of a real-time operating system.