Processes/Process Scheduling Algorithms

Question 1

What is a process

Answer 1

A process is an instance of a program in execution. It is an executing program.

Question 2

Mention Process Management Functions:

Answer 2

PTC - P - DIS - PIM
Process creation
Termination
Controlling the progress of the process

Process

Dispatching
Interrupt handling
Switching between the process

Process synchronization
Inter process communication support
Management of process control blocks

Question 3

Mention and describe the process states

Answer 3

The new state: The process is being created

The running state : The process is executing on the CPU

The blocked state: A process that is waiting for something to complete e.g I/O

The ready state: A process that is ready to be executed, but not currently assigned to a CPU

The terminated state: The process has finished execution.

Question 4

What does a PCB contain?

Answer 4

PCC - MAI
Process state
Program counter
CPU registers
CPU scheduling information
Memory management information
Accounting information
I/O status information.

Question 5

What does the program counter do.

Answer 5

It indicates the address of the next instruction to be executed for this program.

Question 6

Mention and describe the types of context switch

Answer 6

Simple Mode Switch: to process an interrupt without switching process

Full Process Switch: Process is suspended and another process will get the CPU

Question 7

Mention Process Scheduling Queues

Answer 7

Job queue
Ready queue.
Device queues.

Question 8

What is a job queue

Answer 8

Set of all processes in the system

Question 9

What is a job queue

Answer 9

Set of all processes in the system

Question 10

What is a ready queue

Answer 10

Set of all process residing in main memory, ready and waiting to execute

Question 11

What is a device queue

Question 12

What is a device queue

Answer 12

Set of processes waiting for an I/O device. Each device has its own device queue.

Question 13

What is a device queue

Answer 13

Set of processes waiting for an I/O device. Each device has its own device queue.

Question 13

Types of schedulers

Answer 13

Long term schedulers
Short term schedulers

Question 14

Describe the schdulers

Answer 14

Long term scheduler: Also known as the job scheduler it selects which process should be brought into the ready queue.

Short term scheduler - Also known as CPU scheduler: Selects which process should be executed next and allocates CPU.

Question 15

What is a medium term scheduler

Answer 15

Is used to remove processes from memory and reduce the degree of multiprogramming

Question 16

Process can be described as either?

Answer 16

I/O bound process - Spends more time doing I/O than computations

CPU-bound process - spends more time doing computations;

Question 17

What is a dispatcher

Answer 17

An OS program that switches the CPU from one process to another selected by the short term scheduler.

Question 18

Functions of a dispatcher

Answer 18

It prevents a single process from monopolizing the CPU
It decides who goes next according to a scheduling algorithm.

Question 19

What is dispatch latency

Answer 19

It is the time it takes for the dispatcher to stop one process and start another

Question 20

When does a process get terminated

Answer 20

Batch jobs issues
User logs off
Process executes a service request to terminate
Error or fault conditions.

Question 21

What are the scheduling critieria

Answer 21

MAX CPU utilization - keeps the cpu as busy as possible

MAX Throughput - # of processes that complete their execution per unit time

MIN Turnaround time - Amount of time to execute a particular time

MIN Waiting time - Amount of time a process has been waiting in the ready queue.

MIN Response time. - Amount of time it takes from when a request was submitted until the first response is produced, not output

Question 22

What are the CPU scheduling algorithms

Answer 22

First-come First Served(FCFS) Scheduling
Shortest Job First
Priority Scheduling
Round Robin
Multilevel Queue