MIDEXAM(OS)

• Operating System


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


  The software responsible for the management and coordination of activities and the sharing of the resources of the computer
• Operating System


  • Use the computer hardware in an efficient manner
  • Its job is to coordinate the execution of all other software, mainly user applications
• 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
• Users


  People, machines, other computers
• Von Neumann Architecture


  All temporary computer designs are based on this architecture
• Von Neumann Architecture


  • Data and instructions are stored in a single read-write memory
  • Contents of memory are addressable by location
  • Execution occurs in a sequential fashion
• I/O devices and the CPU can execute concurrently
• Device Controller


  A specialized hardware component responsible for managing the operation of specific types of I/O devices
• Local Buffer


  A small amount of memory located within the device controller itself
• Computer System Operation


  1. CPU moves data from/to main memory to/from local buffers

  2. I/O is from the device to local buffer of controller

  3. Device controller informs CPU that it has finished its operation by causing an interrupt
• Components of a Modern OS

  • Storage Management
  • Device Management
  • Memory Management
  • File Management
  • Process Management
  • User Interface
• Storage Management


  Involves organizing and controlling the computer's storage resources
• Device Management


  Controls and coordinates the communication between the operating system and peripheral devices connected to the computer
• Memory Management


  Oversees the allocation, deallocation, and sharing of the computer's memory resources
• File Management


  Organizes and manipulates files and directories stored on the computer's storage devices
• Process Management


  Oversees the creation, scheduling, execution, and termination of processes on the computer system
• Interrupt


  A mechanism used in computer systems to handle events that require immediate attention or priority processing
• Interrupt Service Routine (ISR) / Interrupt Handler


  Responsible for handling the event associated with the interrupt
• Interrupt Handling


  1. The operating system preserves the state of the CPU by storing registers and the program counter

  2. Determines which type of interrupt has occurred (polling or vectored)

  3. Separate segments of code (interrupt service routines) determine what action should be taken for each type of interrupt
• Device-status table


  Contains entry for each I/O device indicating its type, address, and state
• Direct Memory Access (DMA)


  • Used for high-speed I/O devices able to transmit information at close to memory speeds
  • Device controller transfers blocks of data from buffer storage directly to main memory without CPU intervention
  • Only one interrupt is generated per block, rather than one interrupt per byte
• Main Memory


  The only large storage media that the CPU can access directly
• Secondary Storage


  Extension of main memory that provides large nonvolatile storage capacity
• Magnetic Disks


  • Rigid metal or glass platters covered with magnetic recording material
  • Disk surface is logically divided into tracks, which are subdivided into sectors
  • The disk controller determines the logical interaction between the device and the computer
• Caching


  A technique used in computing to temporarily store frequently accessed or recently used data in high-speed storage location
• Asymmetric Multiprocessing


  A multiprocessor computer system where not all of the multiple interconnected central processing units (CPUs) are treated equally
• Symmetric Multiprocessing


  The processing of programs by multiple processors that share a common operating system and memory
• Clustered Systems


  Like multiprocessor systems, but multiple systems working together, usually sharing storage via a storage-area network (SAN)
• Multiprogramming


  • Needed for efficiency
  • Single user cannot keep CPU and I/O devices busy at all times
  • Organizes jobs (code and data) so CPU always has one to execute
  • A subset of total jobs in system is kept in memory
  • One job selected and run via job scheduling
  • When it has to wait (for I/O for example), OS switches to another job
• Timesharing (Multitasking)


  • A logical extension of multiprogramming where the CPU switches jobs so frequently that users can interact with each job while it is running, creating interactive computing
  • Response time should be < 1 second
• Program


  An inactive unit, such as a file stored on a disk
• Program


  A unit of work that has been submitted by the user