Operating System-計算機概論筆記

一定愛配于天立教授開放課程食用:課程連結

Operating System

Batch processing(early era)

• The process of computer operators entering data to the computers and give the result back to you.

Interactive processing(early era)

• OS with remote terminals
• Types of operating system Reference: link
  • Batch(批次)
  • Interactive
  • Real-time
    • Response time is critical.
  • Time-sharing and multitasking
    • Dividing time into intervals.
    • Only one task is being performed at any given time.
  • Multiprocessor
    • Load balancing
    • Scaling
• Software classification
• Shells
  • Communication with users
    • Text based
    • GUI(Graphical user interface )

Kernel

• File manager
  • Directory/folder path
• Device drivers
• Memory manager
  • Allocating main memory
  • Paging, virtual memory
    
• Schedular
  • The component which selects process to execute.
• Dispatcher
  • The component which gives control of CPU to execute the process selected by Schedular.

Linux

• Made by Linus Torvalds
• Freeware and open-source
• Many distribution (Ex: Ubuntu，Kali)
• Linux only means the kernel

How is OS being loaded?

• BIOS(Basic Input/Output Sytem)is usually stored on a EEPEROM chip(Electrically-Erasable Programable Read-Only Memory)

Process

• The activity of executing a program
• Process state
  • Program counter
  • General purpose registers
  • Associated memory cells
• Process table
  • Memory area assigned to the process
  • Priority
  • Ready/waiting(One process for each core)

Process Administration

• Schedular
  • Use: Maintaining the process table
  • Introducing new process
  • Removing completed process
  • Deciding whether a process is ready or waiting
• Dispatcher
  • Use: Getting the process to running state.
  • Controling the allocation of time to the process in the process table.
  • Process switch(interrupt) Multiprogramming between two processes.

Semaphores

• Meaning of semaphore: A visual sinaling appratus with flags, lights...
• Test-and-set: Uninterruptible process, it will change the status of false to true and return it.
• Critical region(臨界區段): A region that is only accessible to a program.
  • Mutual exclusion(互斥鎖): A process that prevents simultaneous access to a shared resource.

Prerequisites for Deadlock

• Deadlock may occur only if all three of the following conditions(necessary but insufficient) are satisfied
  1. Competition for non-shareable resources
  2. Resources are requested on a partial basis, receiving some resources and return later to request more.
  3. Once a resource has been allocated, it cannot be forcibly retrieved.
• To prevent Deadlock from happening, we have to avoid the conditions mentioned above being satisfied.

The Consequence of Preventing Deadlock from Happening

• Starvation: Process cannot get the resources needed for a long time because the resources keep being allocated to other processes.
• The solution to starvation -> (Aging): Adding an aging factor to the priority of each request.