OS Unit 1

• Hardware


  Provides basic computing resources (CPU, memory, I/O devices)
• Operating system


  Controls and coordinates use of hardware among various applications and users
• Application programs


  Define the ways in which the system resources are used to solve the computing problems of the users (word processors, compilers, web browsers, database systems, video games)
• Users


  People, machines, other computers
• Operating system


  A program that acts as an intermediary between a user of a computer and the computer hardware
• Operating system goals


  • Execute user programs and make solving user problems easier
  • Make the computer system convenient to use
  • Use the computer hardware in an efficient manner
• Operating system


  A resource allocator that manages all resources and decides between conflicting requests for efficient and fair resource use
• Operating system


  A control program that controls execution of programs to prevent errors and improper use of the computer
• There is no universally accepted definition of an operating system
• "Everything a vendor ships when you order an operating system" is a good approximation of an operating system definition
• "The one program running at all times on the computer" is the kernel
• Design issues for operating systems

  • Efficiency
  • Robustness
  • Flexibility
  • Portability
  • Security
  • Compatibility
• Efficiency


  The amount of useful work accomplished by the system compared to the time and resources used
• Robustness


  The ability to perform well not only under ordinary conditions but also under unusual conditions that stress its designers' assumptions
• Unix-like operating systems are known for their robustness, as they can operate for prolonged periods without crashing or requiring rebooting
• Flexibility


  The ability to be tailored or changed, either statically or dynamically, to the requirements of specific applications or application domains
• Portability


  The ability of an application to run properly in a different platform to the one it was designed for, with little or no modification
• Categories of dangers to operating system security

  • Security violations
  • Program threats
  • System threats
  • Network threats
• Compatibility


  The capacity for two systems to work together without having to be altered to do so
• Main memory


  The only large storage media that the CPU can access directly, typically volatile
• Secondary storage


  Extension of main memory that provides large nonvolatile storage capacity
• Hard disks


  Rigid metal or glass platters covered with magnetic recording material
• Solid-state disks


  Faster than hard disks, nonvolatile
• Storage systems are organized in a hierarchy based on speed, cost, and volatility

  
• Caching


  Copying information into faster storage system; main memory can be viewed as a cache for secondary storage

  
• Device driver


  Provides uniform interface between controller and kernel to manage I/O
• Direct Memory Access (DMA)


  Allows I/O devices to access main memory directly, without going through the CPU
• Uniprocessor system


  Has one main CPU capable of executing a general-purpose instruction set
• Multiprocessor system


  Has two or more processors in close communication, sharing the computer bus and sometimes the clock, memory, and peripheral devices
• Benefits of multiprocessor systems

  • Increased throughput
  • Economy of scale
  • Increased reliability
• Fault tolerant systems


  Can continue providing service proportional to the level of surviving hardware after a failure of any single component