Operating Systems: Definition and Goals

• An operating system (OS) is software that enables user interaction with computer hardware and acts as the interface between them.
• Operating systems are used everywhere from mobile phones to supercomputers.
• Examples of operating systems include Android, macOS, Linux, Windows, and Unix.

Operating System Goals

• Execute user programs and simplify problem-solving.
• Make the computer system convenient to use.
• Use computer hardware efficiently.

Computer System Organization

• Modern systems involve CPUs and device controllers connected via a common bus.
• This setup allows shared memory access through Direct Memory Access (DMA).
• CPUs and devices can execute concurrently, competing for memory cycles.

Operating System High-Level View

• Users interact with applications.
• Applications rely on the OS for execution
• The OS provides tools and manages application execution on the CPU.
• The OS facilitates application interaction with hardware resources, creating a platform for them to run.

Why Use an Operating System?

• As a front user, the OS is an essential tool to allow interaction with the hardware.
• Provides a user interface (Terminal) for users to interact with machines and instruct them.
• Features a graphical interface with icons for user interaction via a cursor.
• Allows multitasking, so users can run multiple applications simultaneously.
• Examples of multitasking include chatting while watching videos or browsing while listening to music.
• As a programmer, the OS manages input-output operations like printf and scanf in C, without programmers needing to define console display.

Components of the Operating System

• Components can be viewed in two different ways: User View and Kernel View.

Operating System Components in User Mode

• I/O Management.
• Command Interpreter System Management.

Operating System Components in Kernel Mode

• Process Management.
• Memory Management.
• File System & Device Management.
• Security Management.

I/O Management

• Handles inputs from devices like keyboards and mice, and outputs to monitors and printers.
• Translates user input for applications to recognize.
• Manages communication with printers for document printing.

I/O Management Processing Steps

• Input is sent to the OS, which recognizes the input.
• The OS switches from user mode to kernel mode to process the input.
• After processing in the backend, the mode changes back to user mode.
• The result is then displayed.

Command Interpreter System Management

• Inputs are given through GUI (Graphical User Interface) and CLI (Command Line Interface).
• In CLI, commands are interpreted and processed by the operating system to perform tasks.
• Examples of CLI commands include cd, mkdir, cls, and copy.

Process Management

• A process is a running program with allocated resources like RAM, CPU, and I/O.
• Programs become processes when loaded into memory and ready for execution.
• The OS divides programs into multiple processes and allocates resources to each.
• Each process has a Process Control Block (PCB) storing its state.
• The PCB contains a table of attributes related to the process:

Attributes Stored in the PCB

• Process Related: PID (Process Identification Number)
• CPU Related: Registers, program counter, priority states.
• Memory Related: Memory limits, page tables.
• File Related: Files needed for disk access.
• I/O Related: Keyboard, monitors, printers.
• Protection Related: Permissions, Process State Word (PSW).
• Processes transition through different states during execution.

Process States

• New: The process is being created.
• Ready: The process is waiting to be assigned to a processor.
• Running: Instructions are being executed.
• Block/Wait: The process is waiting for some event to occur.
• Suspend Ready: The process is ready but temporarily moved out of main memory.
• Suspend Block: The process is blocked and also moved out of main memory.
• Terminated: The process has finished execution.
• Higher throughput and performance are the reasons for these states.

OS Tasks Related to Processes

• Scheduling: Arranges processes from the new state into a queue for CPU execution.
• Inter-Process Communication: Manages communication between programs with protocols for safety and speed.
• Concurrency: Converts multiple processes into threads, which are executed simultaneously on different CPU cores.
• Deadlock: Occurs when multiple processes are trying to access the same resource, causing each to wait indefinitely for the other.
• Process Synchronization: Addresses conflicts when multiple processes require common resources, preventing the resource from being accessed at the same time to avoid inconsistency issues.
• Semaphores allow processes to communicate before resource access, which is managed by the operating system.

Memory Management

• Handles reading and writing of data to and from main memory.
• Aims to minimize memory wastage and improve utilization.
• Memory Allocation: Manages and allocates memory according to protocols so that memory is not unfairly allocated to any single process leaving memory for others.
• Memory Deallocation: Frees memory occupied by completed processes for reallocation.
• Managing Free Space: Manages free space in the memory to assign to new processes.
• Protection: Prevents processes from accessing memory blocks assigned to other processes.
• Processes are only allowed to acess their own allocated memory blcok.

File System & Device Management

• Every computer system has a disk to store data.
• Disks can be HDDs or SSDs.
• The File System is a method to store and organize files on a disk
• Examples include FAT32 and NTFS.
• Device Drivers: Software written for specific hardware.
• H/W Interface: The hardware port connecting to the hardware, also known as an interface card or controller.
• Interfaces fetch data from the disk, which is identified using the File System.

File System Operations

• Formatting: Applying structure to the disk to store files; often followed by partitioning.
• Partitioning: Dividing a disk into multiple drives or volumes.
• Operations: Include creating, opening, deleting, and modifying files.
• Fragmentation: Inefficient use of storage where small data blocks leave unused space. Disk Scheduling: Queues processes to perform operations in the order the processes are scheduled in.

Disk Scheduling Algorithms

Disk scheduling algorithms include FCFS (First Come First Serve) and SSTF (Shortest Seek Time First).

Security Management

• Security Management is an essential function of the OS
• Security is managed at two levels: User Level and Program Level.

User Level Security

• Authorizes user access to specific files.
• For example guest users cannot access system files.
• Security features apply to applications, such as restricting calculator access to files
• Modern OS includes security applications for threat protection.

Program Level Security

• Prevents a process from accessing another process's memory.
• In C programming, segmentation faults occur when a program tries to access unauthorized memory.
• This helps prevent the corruption of memory.