slides03

Question 1

process

Answer 1

representation of a running program

Question 2

uniprogramming vs multiprogramming

Answer 2

• running more than one program at a time makes better use of time and resources - CPU and I/O not left waiting for chunks of time
• disadvantage of multiprogramming: CPU burns lots of cycles, higher energy usage

Question 2

process structure in memory

Answer 2

1. stack: contains temp data (function parameters, return addresses, local variables)
2. heap: contains dynamically allocated memory during runtime
3. data: contains global variables; initialized data stored at bottom, unitialized data stored on top (takes up less space)
   4.text: where program is loaded in binary

Question 2

CPU bound process

Answer 2

makes heavy use of CPU (eg. computing next prime number)

Question 3

I/O bound process

Answer 3

heavy data processing, need to read/write data from secondary storage

Question 4

process states

Answer 4

1. new: process is being created
2. running: instructions being executed
3. ready: process waiting to be assigned to CPU
4. waiting: waiting for some event (IO)
5. terminated

Question 5

PCB (process control block) (7)

Answer 5

• stores information associated with each process
  1. process state
  2. program counter: address of instruction to execute next
  3. CPU registers
  4. CPU scheduling information
  5. memory management information
  6. accounting information
  7. I/O status information

Question 6

does context switch need a memory save and restore? (3)

Answer 6

1. save all memory onto disk (very time consuming)
2. don’t save memory and trust the next process
3. isolate memory from one process to another; they’re partitioned and don’t share memory space

Question 7

how to create a process?

Answer 7

1. clone an existing process to create a new process using fork() - both user and kernel spaces are cloned
2. mutate the process by loading another program to do required activity using exec() - user space wiped out, kernel space kept the same

Question 8

fork()

Answer 8

• non-zero return value in the parent process (PID of child)
• return value of 0 in child process

Question 9

process termination

Answer 9

• process uses exit() system call to ask OS to delete it
• process’ resources deallocated by OS
• returns status data from child to parent (retrieved in parent using wait())

Question 10

zombie program

Answer 10

• no parent is waiting once a process exits -> no way of recovering process ID

Question 11

processes and address spaces

Answer 11

• processes are isolated - they each have their own address space
• part of the address space is kernel - processes can share through it