[OS] Operating System Structure

• Operating Systems vary greatly in their makeup internally

• COMMONALITIES:

  • Multi-Programming

  • Time Sharing ( Multitasking )

 

1. Multi-Programming

• A single user cannot, in general, keep eigher the CPU or the I/O devices busy at all times
• Multi-programming increases CPU utilization by organizing jobs (code and data) so that the CPU always has one to executed.

Multi-Programmed Systems provide an environment in which the various system resources (for example, CPU, memory, and periphral devices) are utilized effectively, but they do not provide for user interaction with the Computer System.

 

2. Time Sharing ( Multitasking )

• CPU executes multiple jobs by switching among them
• Switches occur so frequently that the users can interact with each program while it is running
• Time sharing requires an interactive (or hands-on ) computer system, which provides direct communication between the user and the system.
• A time-shared operating system allows many users to share the computer simultaneously.

 

Conclusion

• difference Multi-programming vs Multitasking?

  → User interaction with System

• Uses CPU scheduling and multi-programming to provide each user with a small portion of a time-shared computer.

• Each user has at least one seperate program in memory

• A program loaded into memory and executing is called a "PROCESS"

 

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