Operating System - Lecture 1

Operating System - Lecture 1

• Operating system (OS) acts as intermediary between user and computer hardware
• OS goals:
  • Execute user programs efficiently
  • Make the computer system easy to use
  • Use computer hardware efficiently

Topics Covered

• Introduction to OS
• Computer system organization
• OS objectives and functions
• OS services
• Evolution of OS
• System calls
• Types of system calls

Computer System Structure

• Computer system has four main components:
  • Hardware (CPU, memory, I/O devices)
  • Operating system (controls and coordinates hardware use)
  • Application programs (carry out specific tasks)
  • Users (people, machines, other computers)

Four Components of a Computer System

• Users interact with system programs
• System programs interact with operating system
• Operating system interacts with hardware

What Operating Systems Do

• Users want convenience and ease of use
• Don't care about resource utilization
• Users of dedicated systems (workstations) have dedicated resources
• Handheld computers are resource-poor, optimized for usability and battery life
• Some computers have limited or no user interface (embedded computers)

Operating System Definition

• OS is a resource allocator

  • Manages all resources
  • Decides between conflicting requests for efficient and fair resource use

• OS is a control program

  • Controls program execution to prevent errors and improper use

• Kernel: The one program running at all times on the computer

Computer System Organization

• Computer system operation (One or more CPUs, device controllers connect through common bus, access to shared memory)
• Storage structure
• Input/output structure

Computer Startup

• Bootstrap program loads at power-up/reboot
• Typically stored in ROM or EPROM (firmware)
• Loads OS kernel and starts execution
• System processes/daemons run continuously (monitor subsystems)
• Interrupts signal event occurrences (hardware or software)

Common Functions of Interrupts

• Interrupt: External event changing instruction flow.
• Possible solutions for checking interrupts:
  • Polling: CPU periodically checks each device.
  • Interrupt: Interrupt line signals processor; interrupt handler deals with interrupts.

Storage Structures

• Any program needs to be in main memory (RAM)
• RAM is implemented as Dynamic RAM (semiconductor technology)
• Read-Only Memory (ROM) stores static programs (e.g., bootstrap program).
• EEPROM (Electrically Erasable Programmable Read-Only Memory) is used for factory-installed programs (e.g., in smart phones).

Storage Structure

• RAM is volatile
• Secondary storage extends main memory and provides large non-volatile storage capacity (magnetic disks)
• Magnetic disks use rigid platters with magnetic recording material, divided into tracks and sectors.

Storage Hierarchy

• Storage systems are organized in a hierarchy based on speed, cost, and volatility.
• Caching: Copying information to faster storage (e.g., main memory is a cache for secondary storage).

Storage-Device Hierarchy

• Devices are organized in a hierarchy (Registers -> cache -> main memory -> electronic disk -> magnetic disk -> optical disk -> magnetic tapes) of increasing storage capacity, accessibility, speed, and cost.

I/O Structure

• Devices are connected to small computer systems interface (SCSI) controller.
• Devices controlled by device controllers, OS maintains device drivers for each device

Working of Device Controller

• Device controllers have registers and local buffers.
• Direct Memory Access (DMA) is used for bulk data movement.

OS Objectives and Functions

• OS is a layer of software managing devices and providing user programs with a simpler hardware interface.
• OS objectives:
  • Convenience
  • Efficiency
  • Ability to evolve

Layers and Views of Computer System

• Layered approach with end user, application programs, utilities, operating system, programmers and operating system designers.

Layered Approach

• End users interact with applications.
• Applications are developed in programming languages.
• System programs/utilities make applications accessible to hardware.
• OS manages system programs, masks hardware details, provides a convenient user interface.

OS as User/Computer Interface

• OS services include:
  • Program Development (Editors/Debuggers)
  • Program Execution (loading, running, executing)
  • Access to I/O devices (uniform interface)
  • Controlled access to files (file structure, protection)
  • System Access (resource access/conflict resolution)
  • Error Detection
  • Accounting (tracking resource use by users)

OS as Resource Manager

• OS controls basic computer functions (movement, storage, processing of data) and manages resources.

OS as Resource Manager (Continued)

• Resources the OS controls:
  • Main memory
  • I/O devices and files
  • Processor
• OS controls main memory (kernel resides in main memory, contains frequently used functions)
• Main memory allocation done by OS and memory management hardware.

OS as Resource Manager (Continued)

• OS controls input/output (I/O) and files (determining when I/O can be used, controlling file access)
• OS controls processor time allocation.

Explore the fundamentals of operating systems in this first lecture. Learn about the roles and objectives of an OS, its evolution, and the interaction between hardware, system programs, and users. This quiz covers essential components necessary to understand how operating systems function effectively.