We're starting with CPU as a resource, so we need an abstraction of CPU ues. We define a process as the OS's representation of a program in execution so that we can allocate CPU time to it. Note the difference between a program and a process. Multiple processes can be running the same program. The process abstraction turns out to be convenient to hang other resource allocations on.
Processes are the unit of isolation.
Two processes cannot directly affect each other's behavior without making explicit arrangements to. This isolation extends itself to more general security concerns. Processes are tied to users, and the credentials from running on a user's behalf determine what resources the process can use. Process Operatons and Attributes Processes can be created and destroyed. Becuase the're created or destroyed by the CPU, they are created or destroyed by other processes.