Virtualization
Virtualization of resources: Making those who share resources feel that they have independent resources.
Assume there is one physical CPU in a system. What virtualization does is take that single CPU and make it look like many virtual CPUs to the applications running on the system.
For example, CPU virtualization is taking a single CPU in a computer system and making it appear to the processes running on the system that there are separate CPUs. (Illusion)
Virtualization of CPU
The process is; it is a running program.
Computer system actually runs hundreds of process. For example, when we use computers, we could use web browsers like Chrome, listen to music with Spotify, and write documents with Word Processor like Microsoft Word. How could this happen?
Time-sharing
The Operating System provides an illusion to running programs that every process has its own CPU by a technique called time sharing which allows users to run as many concurrent processes as they would like.
Mechanisms and Policy
To implement time sharing well, OS both needs Mechanisms and Policies.
Mechanism means low-level methods or protocols, that implement a needed piece of functionality
Policies are algorithms for making some kind of decision within the OS. For example, given a number of possible programs to run on a CPU, which program should the OS run? A scheduling policy in the OS will make this decision, likely using historical information to make deicisions.