Processes and System calls

Question 1

What is a Process

Answer 1

• A process is a program that’s running
• Program loader,
  invoked by exec( ), retrieves and unpacks executable
• ## Note a thread is a flow of execution within process

Question 2

Processes are defined by their context..

Answer 2

CPU Registers
Memory Layout
Open Files
On-going communication state

Question 3

PCB

Answer 3

Basic Process Control Block holds all the essential management information/context for a process. There’s one PCB per process.
Process state,
Process ID,
Priority

Question 4

Process Hierarchy

Answer 4

• Processes can spawn child processes
• Each child has parent process– Ultimately responsible for resources used by child

Question 5

Creating a Child Process

Answer 5

In Unix this carried out by fork( ) system call– Returns child’s Process ID to parent and 0 to child

Question 6

Process heap

Answer 6

The heap is a part of a process’s memory where it can dynamically request more memory while running — useful when you don’t know in advance how much memory you’ll need.

Question 7

Process Stack

Answer 7

The stack is a part of a process’s memory used to keep track of function calls like a to-do list for the CPU.
- Stack grows and shrinks as functions are called and return.
- On x86 systems, it grows downward
-

Question 8

what is System calls

Answer 8

User programs can’t directly Communicate with (most) hardware as unrestricted access would allow any program to read/ change anything so System Calls Offer standard interface to kernel/ OS functions meaning they communicate to the OS.
System calls Provides access control mechanism Single point of entry that can check all parameter

Question 9

examples of system calls

Answer 9

read() → read data from a file or input

write() → write data to a file or output

fork() → create a new process

exec() → run a new program

exit() → end a process

open(), close() → manage files

Question 10

What happens during a system call?

Answer 10

The program switches to kernel mode, the OS performs the action, then control returns to the program.