Operating System basic terms definition

 

Process state

New         = process is being created

Running     = instructions are being executed

Waiting     = process is waiting for some event to occur

Ready         = process is waiting to be assigned to a processor

Terminated    = process has finished execution

 

Context switch

• when cpu switch to another process, system must save the state of the old process & load the saved state for new process
  
• context switch time is overhead, the system does no useful work while switching
  
• time dependent on hardware support
  

 

Batch processing ( jobs )

• one jobs is executed at a time
  
• programs is a job are executed sequentially
  
• Programs are collected together in a batch before processing starts.
  
• Each piece of work for a batch processing sys is called a job.
  
• Jobs are stored in job queues until computer is ready to process them.
  

 

Real-time ( processes )

• OS interleaves execution of processes in an application program to meet it's deadline
  
• Used when there are rigid time require on the operation of a processor.
  
• Use as a control device in a dedicated sys. (medical imaging)
  

 

Operating System

• program that acts as an intermediary between a user of a computer & the computer hardware
  

 

OS tasks

• maintain list of authorized users
  
• construct a list of all resources in the system
  
• initiate execution of programs
  
• perform scheduling
  
• maintain information for protection
  
• handle requests made by users & their programs
  

 

Virtual memory

• separation of user logical memory from physical memory
  
• allow add spaces to be shared by several processes
  
• allow for more efficient process creation
  
• can be implemented via:-
  
  • demand paging
    
  • demand segmentation
    

 

 

Paging

• logical address space of a process can be noncontiguous
  
  • process is allocated physical memory whenever the latter is available
    
• divide physical memory into fixed-sized blocks called FRAMES (size is power of 2, between 512 byte & 8192 byte)
  
• divide logical memory into blocks of a same sized called PAGES
  
• internal fragmentation
  

 

CPU scheduling

 

Preemptive	Non-preemptive
round-robin shortest job first	FIFO FCFS SJF
Server can be switched to the processing of a new request before completing the current request	a server always processes a schedules request to completion depends on reordering of requests to achieve an improvement in user service or system performance