Proccess Management

Question 1

Define a program

Answer 1

A program is a set of instructions for performing a specific task (passive), and is stored on disk.

when you run it, it is a program associated with a process

Question 2

What is a process

Answer 2

A process is a program in execution (active), and requires CPU resources, primary memory, and I/O.

Question 3

By organising a computer system into processes we achieve what

Answer 3

both modularity (we can switch between them) and improved performance (allowing us to improve performance).

Question 4

What happens in the NEW state of a process lifecycle?

Answer 4

The process is created and enters the system. It awaits admission to the READY state.

Question 5

What happens in the READY state?

Answer 5

The process is prepared to run and waits to be dispatched to the CPU.

Question 6

What happens in the RUNNING state?

Answer 6

The process is actively executing on the CPU.

Question 7

When does a process move to the WAITING state?

Answer 7

A process moves to the WAITING state when it begins I/O operations and waits for I/O to complete.

Question 8

When does a process enter the TERMINATED state?

Answer 8

The process enters the TERMINATED state when it finishes execution and exits.

Question 9

What is the transition from READY to RUNNING called?

Answer 9

The transition is called dispatch, where the CPU scheduler selects a process to run.

Question 10

What happens when a process is paused during execution?

Answer 10

The process transitions from RUNNING back to READY if it’s preempted (e.g., by a higher-priority process).

Question 11

What happens when a process starts an I/O operation?

Answer 11

The process moves from RUNNING to WAITING.

Question 12

What happens when a process completes its I/O operation?

Answer 12

The process transitions from WAITING to READY.

Question 13

What determines the transfer between READY and RUNNING states?

Answer 13

The transfer depends on processor scheduling, which prioritises processes based on their assigned priority.

Question 14

What is a process control block

Answer 14

A Process Control Block (PCB) is a data structure maintained by the operating system to store information about a process. It is used to manage processes during execution.

Question 15

What are the components of the process control block

Answer 15

• Process number
• Process state
• process address space
• process I/O

Question 16

Where is the process control block stored

Answer 16

in the memory or on the disk

Question 17

How to stop running process A and start process B:

Answer 17

1. change the process scheduling state of process A
2. save the context of process A
3. load the context of process B
4. change the process scheduling state of process B

Question 18

What is a context switch

Answer 18

when the CPU switches from running one process to another.

Question 19

What is the tradeoff of context switches

Answer 19

Too few switches lead to poor responsiveness (as it is never actually running the task rather just moving data), while too many switches increase overhead, reducing efficiency.

Question 20

What 4 sections does a process address space have

Answer 20

• a stack for temporary data
• a heap for dynamically-allocated data
• a data for static data
• a text for program code

Question 21

How does a stack work

Answer 21

When a function is called, temporary variables are added to the top of the stack. When exiting a function, these variables are removed from the top of the stack.

Question 22

How does a heap work

Answer 22

In the heap, blocks of memory are allocated and removed in an arbitrary order. The heap is used for variables that need to persist beyond the scope of a single function or need a flexible amount of memory.

Question 23

What is the issue with stack and heap in address space

Answer 23

The stack grows downwards while the heap grows upwards thus they could collide so its up to the OS to stop this by providing more address space

Question 24

What is process calling

Answer 24

A process is created at the request of a different process. In Linux there are four system calls for process spawning.

Question 25

In process spawning, what is the relationship between a parent and child process?

Answer 25

The parent process creates a child process. The child process can execute the same code as the parent or replace its code with a new program using exec.

Question 26

What system call is commonly used to create a new process in Linux?

Answer 26

The fork system call is commonly used to create a new process.

Question 27

What happens when fork is called?

Answer 27

fork creates a child process that is a copy of the parent process, with its own process ID and address space.

Question 28

What are the return values of fork?

Answer 28

The parent process receives the child’s process ID as the return value of fork. The child process receives 0 as the return value.

Question 29

How can a child process run a different program after fork?

Answer 29

The child process can replace its code with a new program using the exec system call.

Question 30

What does the exec system call allow for

Answer 30

The exec system call allows a process to replace its current program with a new executable file.

Question 31

What does the wait system call do

Answer 31

The wait system call causes the parent process to pause execution until the child process completes.

Question 32

What does the exit system call do

Answer 32

The exit system call is issued by the child process when it finishes its task.

Question 33

How may Interprocess communication be implemented

Answer 33

either using: - shared memory - or message passing

Question 34

What is interprocess communication by shared memory

Answer 34

involves processes writing data to/reading data from from an agreed area of memory.

Question 35

What is interprocess communication by message passing

Answer 35

involves processes sending messages to/receiving messages from an agreed mailbox.

Question 36

Shared Memory vs message passing

Answer 36

Message passing requires regular system calls, while shared memory only requires system calls to set up the shared memory space. As a result, shared memory is generally more efficient for large data transfers, whereas message passing is better suited for smaller data exchanges.

Question 37

When does a process move into the running state

Answer 37

When the schedueler decides to exeter the program it move to the running state.