Operating Systems

Question 1

What is a multi programmed batch, and how did it improve from batch OS?

Answer 1

Multi-programmed batch OS takes in and runs multiple types of jobs at a time, in “batches.” It does so by filtering through a job pool.

Improvements: Less CPU idle time and faster run time.

Question 2

What is a PCB? How is it important to muti-program batch?

Answer 2

PCB (Process Control Block).
It is important for MPB because it helps jobs(processes) be resumed/paused smoothly, making switching between jobs a more efficient process.

Question 3

PCB Components:

Answer 3

-Context Data
-Process ID
-Priority
-User Account Info
-Processing State

Question 4

Context Data:

Answer 4

Pointers, registers used, and other information that is stored in a PCB to better understand the process running and to help resume/pause a program.

Question 5

Process ID:

Answer 5

ID to identify a process.

Question 6

Priority

Answer 6

“Height of importance” of a process.

Question 7

User Account Info:

Answer 7

Identifying information of the user who sent the program.

Question 8

Processing State:

Answer 8

(Running, wait, I/O, ready…)

Question 9

Difference between process and program

Answer 9

Process is a set of instructions in an active state, actively used by the CPU. Program is passively stored instructions, waiting in memory to be run.

Question 10

Define PCB:

Answer 10

A block of memory created when a process is created. It is designed to store any relevant information about the instructions in a process. Processes that are created and sent to job pool.

Question 11

What actions can be taken on a process?

Answer 11

Processes can be: created, terminated, suspended, and interrupted.

Question 12

Before New Queue:

Answer 12

Program has to be pulled from memory.

Question 13

Before Ready Queue:

Answer 13

Creation of process and PCB, scheduled by long-term.

Question 14

Before Run Queue:

Answer 14

Scheduled by short-term scheduler.

Question 15

Before Wait Queue:

Answer 15

An event is triggered that needs I/O or another response from the computer.

Question 16

Run to Ready:

Answer 16

A flag is marked somewhere in the instructions, causing the process to be paused.

Question 17

Wait to Ready:

Answer 17

The event that caused the process to be put in wait queue is done.

Question 18

Run to Terminate:

Answer 18

The last instruction is completed, and any memory/data used by the processor is returned to computer.

Question 19

Long term scheduler:

Answer 19

Picks with jobs to be sent to ready queue. Rarely used.

Question 20

Short term scheduler:

Answer 20

Picks which process to be run. Frequently used.

Question 21

Processing sorting algorithms:

Answer 21

First Come, First Served
Shortest Job First
Round Robin

Question 22

With sorting algorithm is the most efficient from a CPU usage standpoint?

Answer 22

Round Robin

Question 23

Response Time:

Answer 23

1st time in run queue - arrival time

Question 24

Turnaround Time:

Answer 24

Termination time - arrival time

Question 25

FC,FS:

Answer 25

Whatever enters the processor first, gets completed first

Question 26

SJF:

Answer 26

When jobs arrive, the shortest job (by CPU bursts) is completed first.

Question 27

RR:

Answer 27

Switches between each process by cutting CPU bursts down by a “time quantum” (a specific number).

Question 28

Batch system uses which algorithm?

Answer 28

FCFS. Batch system handles one job at a time as it is received.

Question 29

Multi-Programmed Batch uses which algorithm?

Answer 29

SJF. Multi-Programming handles a job pool, holding many jobs at once before it is sent to the run queue.

Question 30

Time Sharing uses which algorithm?

Answer 30

RR. It equally divides CPU time between multiple processes.

Question 31

Strengths and Weaknesses of SJF (pre-emptive)

Answer 31

Strengths: Shortest average response time and average turnaround time. Weaknesses: More possibility of OS over-heading. Long CPU idle time for some processes. Processes could take forever to finish.

Question 32

CPU burst:

Answer 32

The time that CPU is used before a process is sent to I/O or process is terminated.

Question 33

Time Quantum:

Answer 33

A number (of CPU burst time) used in Round Robin scheduling algorithm that should allow at least half of processes to be completed.

Question 34

With a high time quantum number, what is the risk?

Answer 34

Average Turnaround and average response time will suffer.

Question 35

With a low time quantum number, what is the risk?

Answer 35

A high chance of CPU overhead.

Question 36

Symbol Table:

Answer 36

holds operation codes (symbols) to perform the intended calculation and/or algorithm.

Question 37

Instruction Code:

Answer 37

All instructions of a process written in machine code (0/1).

Question 38

Functions:

Answer 38

Similar to instruction code, more machine code based on processes’ written functions.

Question 39

Stack Space:

Answer 39

Where temporary registers/data reside while process runs and until process is completed.

Question 40

PCB:

Answer 40

Holds all process information needed to identify and manipulate how it runs.