Operating System Lecture 1-2: Introduction

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Reference

• Topics covered:
  • Introduction to Operating System
  • Process Management
  • CPU Scheduling
  • Deadlocks
  • Memory Management
  • I/O Systems
  • Protection and Security

What is an Operating System?

• Definition: A program that acts as an intermediary between a computer user and the computer hardware.
• Goals:
  • Execute user programs to simplify problem-solving.
  • Make the computer system convenient to use.
  • Utilize computer hardware efficiently.
• Kernel: The core program running at all times on the computer.
• Programs:
  • System programs: Included with the operating system.
  • Application programs: All other programs.

Computer System Structure

• Hardware: Provides basic computing resources (CPU, memory, I/O devices).
• Operating System: Manages resource usage to solve user computing problems (e.g., word processors, compilers, web browsers, databases, video games).
• Users: People, machines, or other computers interacting with the system.

Services Provided by Operating Systems

1. Program Execution:
   • Loads programs into memory and runs them.
   • Supports normal or abnormal (error) termination.
2. I/O Operations:
   • Manages input/output for programs, as users cannot directly control I/O devices for efficiency and protection.
3. File-System Manipulation:
   • Enables programs to read, write, create, delete, and search files and directories.
   • Includes permissions management for access control.
4. Communications:
   • Facilitates information exchange between processes, either on the same computer (via shared memory) or across networked systems (via message passing).
   • Shared Memory: When two or more processes read and write to a shared section of memory.
   • Message Passing: When packets of information in predefined formats are moved between processes by the operating system.
5. Error Detection:
   • Continuously detects and corrects errors in:
     • CPU and memory hardware (e.g., memory errors, power failures).
     • I/O devices (e.g., disk parity errors, network failures, printer issues).
     • User programs (e.g., arithmetic overflow, illegal memory access, excessive CPU usage).
6. Resource Allocation:
   • Manages resources for multiple users or jobs, allocating CPU, memory, and I/O devices.
7. Accounting:
   • Tracks resource usage by users for monitoring and optimization.
8. Protection and Security:
   • Ensures controlled access to system resources.
   • Authenticates users and defends against invalid access attempts, including external I/O devices and network adapters.

Historical Overview

Mainframe Systems

• Overview: First computers for commercial and scientific applications.
• Batch Systems:
  • Large machines operated via consoles.
  • Input: Card readers, tape drives.
  • Output: Line printers, tape drives, card punches.
  • Users submitted jobs (punch cards) to operators, with no direct interaction.
  • OS was simple, transferring control between batched jobs with similar needs for efficiency.
• Multiprogrammed Systems:
  • Multiple jobs in memory, with CPU multiplexed among them.
  • OS switches to another job when one waits (e.g., for I/O).
• Time-Sharing Systems:
  • Extension of multiprogramming, with frequent CPU switching for user interaction.
  • Supports multiple users simultaneously via mouse/keyboard input.

Personal Computer Systems

• Dedicated to a single user.
• I/O devices: Keyboards, mice, displays, small printers.
• Prioritizes user convenience and responsiveness.
• May not require advanced CPU utilization or protection features.

Multiprocessor Systems (Parallel Systems)

• Overview: Multiple CPUs in close communication, sharing memory and clock.
• Advantages:
  • Increased throughput (more work in less time).
  • Cost-effective (shared peripherals, storage, power).
  • Improved reliability (system continues if one processor fails).
• Types:
  • Symmetric Multiprocessing (SMP): Each processor runs an identical OS copy, supporting multiple processes without performance loss.
  • Asymmetric Multiprocessing: Master processor assigns tasks to slave processors, common in large systems.

Distributed Systems

• Computation distributed across multiple processors with local memory.
• Loosely coupled, communicating via high-speed buses or networks.
• Advantages:
  • Resource sharing.
  • Computation speedup through load sharing.
  • Enhanced reliability.
  • Improved communication.

Computer System Organization

• Operation:
  • CPUs and device controllers connect via a common bus to shared memory.
  • Concurrent execution of CPUs and devices, competing for memory cycles.
• I/O Operations:
  • CPU and I/O devices execute concurrently.
  • Device controllers manage specific devices with local buffers.
  • CPU moves data between main memory and controller buffers.
  • Controllers signal completion via interrupts.

Interrupts

• Function: Transfer control to interrupt service routines via an interrupt vector.
• Types:
  • Hardware interrupts: Triggered by signals to the CPU.
  • Software interrupts: Triggered by system calls.
• Process: Saves the address of the interrupted instruction.

Digital Data Representation

• Bit: Smallest data unit (1 or 0).
• Byte: 8 bits, used to measure file and program sizes.
• Prefixes:
  • Kilobyte (KB): $2^{10}$ bytes (1024 bytes).
  • Megabyte (MB): $2^{20}$ bytes (1024 KB).
  • Gigabyte (GB): $2^{30}$ bytes (1024 MB).
  • Terabyte (TB): $2^{40}$ bytes (1024 GB).
  • Petabyte (PB), Exabyte (EB), Zettabyte (ZB), Yottabyte (YB) follow similarly.

Storage Hierarchy

• Organized by speed, cost, and volatility.
• Caching: Copies data to faster storage (e.g., main memory as a cache for secondary storage).
• Device Drivers: Provide a uniform interface between controllers and the OS kernel.

Storage Structure

• Main Memory:
  • Only storage directly accessible by the CPU.
  • Random access, typically volatile.
• Secondary Storage:
  • Extends main memory with large, nonvolatile capacity.
  • Hard Disks: Magnetic platters divided into tracks and sectors.
  • Solid-State Disks (SSDs): Faster, nonvolatile, increasingly popular.
• Disk Controllers: Manage logical interactions between devices and the computer.

Caching

• Copies data from slower to faster storage temporarily.
• Process:
  • Check cache first; use data if present (fast).
  • If absent, copy data to cache for use.
• Challenges:
  • Cache size and replacement policy are critical design considerations.
  • Cache is smaller than the storage it caches.