Summary: Operating Systems

Read the summary and the most important questions on Operating Systems

• Chapter 1: Introduction

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• What is an operating system?

  A program that acts as an intermediary between a user of a computer and the computer hardware

• What are 3 goals of an operating system?

  1. Execute user programs and make solving user problems easier
  2. Make the computer system convenient to use
  3. Use the computer hardware in an efficient manner 

• Computer systems can be divided into 4 parts - what are these parts?

  1. Hardware - provides basic computing resources (CPU, memory, I/0 devices) 
  2. Operating system - controls and coordinates use of hardware among various applications and users
  3. Application programs - define the ways in which the system resources are used to solve the computer problems of the users (e.g. word processors, compilers, web browsers, database systems, video games)
  4. Users - people, machines, other computers

• What does the bootstrap program do?

  It helps the computer startup
  - BP is loaded at power-up or reboot
  - Typically stored in ROM  
  - Initialises all aspects of the system
  - Loads operating system kernal and starts execution
  - The bootstrap allows the sequence of programs to load in order to initiate the OS

• How does a device controller inform the CPU that it is finished its operation?

  The device controller causes an interrupt 
  
  (each device controller is in charge of a particular device type)
  (there is a device driver for every device controller)
  
  IMPORTANT POINT: An interrupt will not wait for any other CPU routine to complete. It can be raised even in the middle of CPU execution

• What are common functions of interrupts?

  
  
  
  
  

  • Interrupt transfers control to the interrupt service routine (ISR) generally, through the interrupt vector, which contains the addresses of all the service routines
    
  • Interrupt architecture must save the address of the interrupted instruction
    
  • A trap or exception is a software-generated interrupt caused either by an error or a user request
    
  • Interrupts are handled much like calling a function in a programming language
    
  • Most operating systems are interrupt driven 
    

• What is the main memory and what are its characteristics?

  Main memory - storage media that the CPU can access directly
  

  • Random access 
    
  • Typically volatile (loses its content when power is turned off)
  • Usually too small to store all needed programs and data permanently 

• What is secondary storage?

  Extension of main memory that provides large nonvolatile storage capacity

• What are solid-state disks (SSDs)

  - Faster than hard disks 
  - nonvolatile 
  
  - there are no moving parts involved

• What is a cache?

  A place to store something temporally in a computing environment
  - information in use is copied from slower to faster storage temporarily