Computer Systems Fundamentals - Notes

Operating Systems Overview

• Definition: Operating systems (OS) control the operation of hardware in a computer.
• Every computer requires an OS.
• Roles of Human Users: The OS acts as the intermediary between the user and the hardware, functioning much like a king or director overseeing computer operations.
• Types of Operating Systems: Different OS types exist for various purposes, each tailored to specific hardware and user needs.
• Functions of OS:
  • File Management: Handling data storage and file systems.
  • Memory Management: Allocating and managing memory resources.
  • Process Management: Overseeing the execution of processes.
  • Input/Output Functionality: Managing device input and output.
  • General Purpose Functions: Providing system information such as system status and user resources.

Operating System Interactions

• OS interacts with different components:
  • Human Users
  • Application Software
  • Other System Software
  • Hardware

Types of Operating Systems

• Classification Criteria:
  • Type of hardware they run on.
  • Number of programs that can be active simultaneously.
  • Type of interaction allowed.
• Microcomputer OS Requirements:
  • Initialize the system, manage memory, and data transfer between peripherals.
• Minicomputer OS Requirements:
  • Support for resource sharing and multi-user systems.
• Mainframe Computer OS Requirements:
  • Capability to run multiple programs and handle input/output through dedicated controllers.

Operating System Types

• Single-Programmed OS: Where one process is executed at a time (e.g., MS-DOS).
• Multi-Programmed OS: More than one process in memory at once, capable of resource sharing and user protection (e.g., Windows).
• Batch Processing System: Efficiencies where jobs are submitted in batches without user interaction.
• Interactive System: Users can interact with processes, with options for single or multi-user environments.
• Real-Time Systems: Built for time-critical applications such as telecommunications and air traffic control.

Functions of the Operating System

• Principal Functions:
  • File Management: Handling filenames, directories, and files as collections of related data.
  • Process Management: Creating, scheduling, and terminating processes, as well as managing inter-process communication.
  • Memory Management: Allocating, deallocating, and protecting memory usage between processes to prevent conflicts.
  • Input/Output Functionality: Converting user requests into actions for input/output operations.
  • General Purpose Functions: Managing system information including process queues and system timestamps.

Process Management

• Process Lifecycle:
  • A process is an instance of a program in execution needing CPU resources.
  • States of a process include: New, Ready, Running, Waiting, Terminated.
• Scheduling Approaches:
  • First Come, First Served (FCFS): Processes execute in order of arrival.
  • Shortest Job Next (SJN): Selects the shortest process to execute next.
  • Round Robin: Uses time slices to provide fair CPU time among processes.

Memory Management

• Concepts:
  • Logical vs. Physical Addressing: Logical addresses are generated by the CPU, while physical addresses refer to actual memory locations.
  • Memory Partitioning: Fixed-size vs. Variable-size allocation methods to manage memory effectively.
  • Memory Management Techniques:
  • Best-Fit Method: Allocates memory to the smallest suitable partition to minimize wasted space.
  • Worst-Fit Method: Allocates to the largest hole in memory to maximize usable large spaces.
  • First-Fit Method: Allocates the first available space that is sufficient, though it may lead to fragmentation.
• Paged Memory Management: Divides processes into pages of fixed size, tracked by a Page-map Table (PMT).
  • Demand Paging: Pages are loaded into memory as needed.
  • Swapping / Virtual Memory: Utilizes hard disk space as an extension of RAM when processes exceed available memory.