Processes1

Question 1

What is a process?

Answer 1

When a program is executed and loaded into the memory. It is an active entity. A program may create multiple almost identical processes.

Question 2

What is a program?

Answer 2

Passive entity (executable file) stored on HDD

Question 3

What is process context?

Answer 3

A process contains text section (program code), current activity (process number, process state, program counter, value stored in registers, CPU related information, Accounting information and I/O status information), stack (temporary data), data section (global data that is shared between processes), heap (memory allocated).

Question 4

What is a PCB?

Answer 4

Process Control Block. Each process has its own PCB. PCB contains the context information about a process.

Question 5

What is a process Identification Number PID?

Answer 5

Process Identifier is the unique ID number to identify a process.

Question 6

What are the different process states?

Answer 6

A process can be in 5 possible states: new (created), running (executed), waiting, ready (waiting to be assigned to CPU) and terminated (finished).

Question 7

What is contained in the program counter?

Answer 7

The location of instruction that CPU needs to execute next.

Question 8

Whats an idle process?

Answer 8

Process waiting for I/O to complete

Question 9

What is context switching?

Answer 9

When CPU is switching from Process 0 to Process 1, CPU will first save the current state/context of Process 0 to Process 0’s PCB. It will then load the state/context of Process 1 from Process 1’s PCB.

Question 10

What is a foreground process?

Answer 10

Process that is currently visible to the user and controlled via user interface.

Question 11

What is a background process?

Answer 11

Process that is currently running in memory but are not on display.

Question 12

How are processes created?

Answer 12

Process is created because of an execution of a system call, initiation of a batch job, a user request to create a new process and a running process create one or more new child processes.

Question 13

what does the fork() system call do?

Answer 13

System call to create a new process

Question 14

What does the exec() system call do?

Answer 14

System call to load a new program to the specified process

Question 15

What are the resource sharing options for processes?

Answer 15

A child process may share all, subset or none of the parent’s resources. Usually a child process only share subset of the parent to prevent a process overloading the system with too many child processes.

Question 16

What are the different options for processes to exectue?

Answer 16

A child process may be executed concurrently with the parent, or the parent usually waits until the child process is terminated.

Question 17

What does the exit()system call do?

Answer 17

System call to indicate OS that the process has finished executing all of its program and OS may delete it from the RAM.

Question 18

What does the wait()system call do?

Answer 18

Parent process is waiting for child process to send its output.

Question 19

What does the abort system call do?

Answer 19

A process is terminated before it has finished executing all of its program.

Question 20

What is an abnormal termination?

Answer 20

A process is terminated abruptly before it has finished executing all of its program. This may happen due to programming error, run-time error, I/O error, parent process kills it, or user intervention.

Question 21

What is an Interrupt (Error exit)?

Answer 21

If a process is abruptly terminated because it has encountered an error that the program has anticipated. Instead of just exiting the process without any information, the process will provide user with some details about the cause of the abnormal termination and possible ways to solve the error.

Question 22

What is a fatal error?

Answer 22

If a process is abruptly terminated because it has encountered an error that the program has not anticipated. Generally, the process will exit without providing any information to user.

Question 23

How can a child process be terminated?

Answer 23

A child process may be terminated by its parent because it has exceeded its usage of some of the allocated resources, the task assigned to child is no longer required or because the parent has been terminated and the OS does not allow a child to continue.

Question 24

What is a cascading termination?

Answer 24

A child process is terminated because its parent has been terminated.

Question 25

What is a zombie process?

Answer 25

When a child process is terminated but it has no parent waiting to collect its output.

Question 26

What is an orphan process?

Answer 26

When a child process is still running even when the parent has been terminated.

Question 27

What are the different parts of a process?

Answer 27

The program code, called text section

Current activity including Program counter, processor registers

Stack containing temporary data

Data section containing global data (shared between processes)

Heap containing memory allocated during run-time

Question 28

What is the stack?

Answer 28

Used for static memory allocation
Very fast & local access (local variables), limited size
LIFO order (Last In First Out)
Automatically managed
Know exactly how much data you need to allocate before compiling

Question 29

What is the heap?

Answer 29

Used for dynamic memory allocation
Global access
Manually managed (malloc(), calloc(), free(), delete() systems calls)
Don’t know exactly how much data you need at runtime

Question 30

What info is stored in a PCB?

Answer 30

Process number and state

Program counter – location of instruction to next execute

CPU-related information

Memory-management information – memory allocated to the process

Accounting information – CPU used, clock time elapsed since start, time limits

I/O status information – I/O devices allocated to process, list of open files