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Lecture 2 Processes
Lecture 1 Introduction


Operating Systems


Harris Chikunya

Learning Outcomes

By the end of this Lecture, you should be able to:

• Explain the concepts of process, various states in the process and their scheduling;

Define a process control block;

• Classify three types of schedulers;

• Explain five types of scheduling algorithms; and

• Compare the performance evaluation of the scheduling algorithms.

Concept of Process

  • A process is a sequential program in execution
  • It defines the fundamental unit of computation for the computer
  • Components of process are:
  • Object Program – code to be executed
  • Data – is used for executing the program
  • Resources – while executing the program, it may require some resources
  • Status of the process execution – used for verifying the status of the process execution.

Process vs Program


  • Is a dynamic entity i.e a program in execution
  • Is a sequence of information executions
  • Exists in a limited span of time
  • Two or more processes could be executing the same program, each using their own data and resources
  • Program

  • Is a static entity made up of program statements
  • Contains the instructions
  • A program exist at place in space and continues to exist
  • Does not perform the action by itself.

Process State

  • As a process executes, it changes state
  • The state of a process is defined by the current a activity of that process
  • The process may be in one of the following states
  • New – a process that just been created
  • Ready – processes waiting to have the processor allocated to them by the OS so that they can run
  • Running – process that is currently being executed
  • Waiting – a process that cannot execute until some event occurs such as the completion of an I/O operation
  • Terminated – The process has finished execution

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