Processes & Threads

Question 1

What are CPU activities called?

Answer 1

• A batch system executes jobs
• A time-shared system had user programs or tasks
• Common term for all processes

Question 2

What are programs?

Answer 2

• A program is a passive entity, stored on disk (or other media).
  waiting to be executed
• Once active, we refer to its instantiation as a process
• Single programme: may invoke multiple individual processes

Question 3

What does Text Segment (Code) store?

Answer 3

• Stores the executable code

Question 4

What does Data Segment store?

Answer 4

Stores global and static variables

Question 5

What does the Heap segment do?

Answer 5

Used for dynamic memory allocation at
run time
* Grows upward in memory as more
memory is allocated.
* Shrinks when memory is freed

Question 6

What is the Stack Segment?

Answer 6

• Temporary data
• Stores function calls, local variables, and return addresses.
• Grows downward in memory.
• Each function call creates a new stack frame.

Question 7

What are the 5 step that a OS manages New Process?

Answer 7

Typical steps OS follows when creating a process
1. Allocates memory
2. Assigns a unique Process ID (PID)
3. Loads executable code into memory
4. Sets up the process’s execution context – PCB etc.
5. Schedules the process for execution

Question 8

What is the Scheduling Processes aim?

Answer 8

To maximise CPU usage

Question 9

What are the 4 (Scheduling Processes)

Answer 9

• Job queue (long-term scheduler)
• Ready queue (short-term scheduler)
• Device queue (for each device)
  
  • I/O requests awaiting completion
• Swapped-out queue (medium-term scheduler)
• Management of processes that cannot make progress towards
  completion
• Free up space for other processes

Question 10

To manage and control processes, OS must know what?

Answer 10

• Process location
• Process attributes

Question 11

What is IPC?

Answer 11

Inter-Process Communication (IPC) is a mechanism that
allows processes to communicate and share data.
* Processes run independently and have separate memory
spaces
* IPC enables them to exchange information efficiently.

Question 12

Why is IPC needed?

Answer 12

Processes often work together - need to share data.
* Some processes depend on each other’s output
* e.g., a producer process creates data, and a consumer process
uses it
* Processes need to synchronise their execution (e.g., avoiding
race conditions)

Question 13

What are Threads?

Answer 13

A thread or lightweight process is a particular execution
path within a larger process
* They share the process’s resources (memory, files, etc.)
* They have independent execution flows.

Question 14

Multithreading Benefits

Answer 14

Responsiveness
* May allow a program to continue running even if part of it is blocked or performing
a lengthy operation

Resource sharing
* Processes can only share resources through techniques such as shared memory
and message passing.
* Threads share the memory and resources of the process by default

Economy
* Allocating memory and resources for process creation is costly.
* Threads share the resources of the process. Thus, it is more economical to create
and context-switch threads.

Scalability
* A single thread process can only run single core
* Multi thread process can run in parallel across multiple cores