Lecture 1 - Introduction

Instructor: Michael Swift & Tej Chajed Topics: What is an OS, OS abstractions, virtualization, concurrency, persistence, OS history

Learning Objectives

• Understand the purpose of the operating system
• Understand the position of the operating system in a computer running applications
• Understand the evolution of operating systems

What is an Operating System?

Operating System (OS): A software layer to abstract away and manage details of hardware resources; a set of utilities to simplify application development.

• “All the code you didn’t write” in order to implement your application

graph TD
    A[Applications] --> B[OS]
    B --> C[Hardware]

The OS and Hardware

• An OS mediates programs’ access to hardware resources
  • Computation (CPU)
  • Volatile storage (memory) and persistent storage (disk, etc.)
  • Network communications (TCP/IP stacks, ethernet cards, etc.)
  • Input/output devices (keyboard, display, sound card, etc.)
• The OS abstracts hardware into logical resources and well-defined interfaces to those resources
  • Processes (CPU, memory)
  • Files (disk)
    • Programs (sequences of instructions)
  • Sockets (network)

Why Use an OS?

Application Benefits

• Programming simplicity
  • See high-level abstractions (files) instead of low-level hardware details (device registers)
  • Abstractions are reusable across many programs
• Portability (across machine configurations or architectures)
  • Device independence: 3Com card or Intel card?

User Benefits

• Safety
  • Program “sees” its own virtual machine, thinks it owns the computer
  • OS protects programs from each other
  • OS fairly multiplexes resources across programs
• Efficiency (cost and speed)
  • Share one computer across many users
  • Concurrent execution of multiple programs

What Functionality Belongs in an OS?

• No single right answer
  • Desired functionality depends on outside factors
  • OS must adapt to both user expectations and technology changes
    • Change abstractions provided to users
    • Change algorithms to implement those abstractions
    • Change low-level implementation to deal with hardware
• Current operating systems are driven by evolution

Major Themes in OS

Virtualization

• Taking physical hardware and making a software version that is sharable, easier to use, more powerful
• Examples:
  • CPU: We can run two programs at the same time
  • Memory: Programs see a linear range of addresses but underlying DRAM is shared in 4KB chunks
  • Disk: We use files/folders, disk internally has blocks

Concurrency

• Maintaining correctness when many things happen at once
• Examples:
  • Code on 2 CPUs try to increment the same variable

Persistence

• Keep data safe across system crashes/reboots

History of Operating Systems

Related

• Navigation: Lecture 2 →
• Exam: Midterm 1
• Course: CS 537 Map of Content