Multiprogramming & Timesharing | Computer System Structure | Operating System | L 8

Multiprogramming The operating system keeps several jobs in memory simultaneously Generally Main memory is too small to accommodate all jobs. So the jobs are kept initially on the disk in job pool which consist of all processes on disk awaiting allocation of main memory Set of jobs in memory can be a subset of the jobs kept in the job pool Operating system picks and begins to execute one of the jobs in memory Eventually, the job may have to wait for some task, such as an I/O operation, to complete In a non-multiprogrammed system, the CPU would sit idle In a multiprogrammed system, the operating system simply switches to, and executes, another job when that job needs to wait, the CPU switches to another job, and so on Eventually, the first job finishes waiting and gets the CPU back As long as at least one job needs to execute, the CPU is never idle Advantage: Better system resource utilization Disadvantage : No User Interaction Timesharing Time sharing (or multitasking) is a logical extension of multiprogramming CPU executes multiple jobs by switching among them, but the switches occur so frequently that the users can interact with each program while it is running Time sharing requires an interactive computer system, which provides direct communication between the user and the system The user gives instructions to the operating system or to a program directly, using a input device such as a keyboard, mouse, touch pad, or touch screen, and waits for immediate results on an output device Accordingly, the response time should be short—typically less than one second A time-shared operating system allows many users to share the computer simultaneously Since each action or command in a time-shared system tends to be short, only a little CPU time is needed for each user A time-shared operating system uses CPU scheduling and multiprogramming to provide each user with a small portion of a time-shared computer Each user has at least one separate program in memory A program loaded into memory and executing is called a Process When a process executes, it typically executes for only a short time before it either finishes or needs to perform I/O & I/O may be interactive Interactive I/O typically runs at “people speeds,” it may take a long time to complete So operating system will rapidly switch the CPU to the program of some other user #operatingsystemtutorials #operatingsystemplaylist #ostutorial #osplaylist #os #multiprogramming #dualmodeoperations #usermode #osmode #kernelmode #modebit #operatingsystems #parallelsystems #operatingsystemvideos #operatingsystemtutorials #operatingsystemplaylist #operatingsystemlectures #cseguru #cseguruvideos #cseguruosvideos #csegurututorials CSEGuru Videos #CSEGuru Compiler Design Videos: https://www.youtube.com/playlist?list=PLLykrwdi1zxExCT-6TBYkYhrRuWnnQFML CSEGuru DAA Videos https://www.youtube.com/playlist?list=PLLykrwdi1zxF22UVdcQnbiMfSOBTOiGVq CSEGuru Operating System Videos https://www.youtube.com/playlist?list=PLLykrwdi1zxENpYpQsaOSwquHGWXW0cfB CSEGuru Gate cse Videos https://www.youtube.com/playlist?list=PLLykrwdi1zxGlZpM7mHkKVh_Wytgw9lQ0 CSEGuru NET cse Videos https://www.youtube.com/playlist?list=PLLykrwdi1zxFJr5nT-xHMC4JWovtHSLuL CSEGuru Data Structure Videos https://www.youtube.com/playlist?list=PLLykrwdi1zxF0ezo6NCzrAW4nZ6zDl6k6 CSEGuru Sorting Algorithm Videos https://www.youtube.com/playlist?list=PLLykrwdi1zxFOkDhPnPeoPfRcXegcJ4bt