-> A process is just an executing program, including the current values of the program counter, registers, and variables.
-> Conceptually, each process has its own virtual CPU.
-> In reality, the real CPU switches back and forth from process to process, but to understand the system, it is much easier to think about a collection of processes running in (pseudo) parallel, than to try to keep track of how the CPU switches from program to program.
-> This rapid switching back and forth is called multiprogramming and the number of processes loaded simultaneously in memory is called degree of multiprogramming.
-> In any multiprogramming system, the CPU switches from process to process quickly, running each for tens or hundreds of milliseconds.
-> While, strictly speaking, at any one instant the CPU is running only one process, in the course of 1 second it may work on several of them, giving the illusion of parallelism.
-> Sometimes people speak of pseudoparallelism in this context, to contrast it with the true hardware parallelism of multiprocessor systems (which have two or more CPUs sharing the same physical memory).
Post a Comment