4. The Abstraction: The process

Question 1

How does OS virtualize CPU? How is this technique called?

Answer 1

By running one process, then another, then another and so forth. This is called time-sharing of the CPU.

Question 2

What makes decision on which process to run next?

Answer 2

Scheduling policy

Question 3

What is an opposite of time-sharing?

Answer 3

Space-sharing.

Question 4

What is a process? What are its parts?

Answer 4

An abstraction provided by an OS of a running program. Its parts are address space, registers, I/O information

Question 5

What are the common registers used by process?

Answer 5

General purpose registers, program counter (or instruction pointer), stack pointer (used to store and remove data) and associated frame pointer (used to find where specific function starts in stack)

Question 6

What is minimally expected from Process API?

Answer 6

Create, Destroy, Wait, Status, Miscellaneous Control functions.

Question 7

How is process created?

Answer 7

OS loads program’s code and any static data into memory in address space of a process, memory is allocated for stack and heap; and I/O descriptors are set up. Then main() of program is started.

Question 8

Which data structure does OS use to track state of the processes? What is a data structure with information about single process?

Answer 8

Process list. Process Control Block (sometimes called process descriptor)

Question 9

Why it might be a good idea to run a process that issued an I/O immediately after I/O finishes?

Answer 9

Because it might issue another I/O operation and other processes will run while the first process is again blocked with I/O.