Chapter 1.1 Lock-in

ACompressed recap

Process = text, data, heap, stack + PCB (PID, state, PC, registers, open files). States New, Ready, Running, Waiting, Terminated; no Waiting → Running or Ready → Waiting. fork: 0 to child, PID to parent, copied memory; 2ⁿ processes from n forks; loops add per iteration. Zombie, orphan; context switch overhead; long/short/medium-term schedulers.

BMerged rule card

1.1.1 Processes: memory layout, process control block and process states

• Process memory: text (code), data (globals), heap (dynamic, grows up), stack (calls, grows down).
• PCB: PID, state, program counter, registers, scheduling info, memory info, open files, accounting.
• States: New, Ready, Running, Waiting, Terminated.
• Transitions: admit, dispatch (Ready→Running), pre-empt (Running→Ready), I/O request (Running→Waiting), event done (Waiting→Ready), exit. Waiting→Running and Ready→Waiting are impossible.
• Suspended-ready / suspended-waiting via swapping.

1.1.2 Creating processes with fork(), exec() and wait(); context switches and schedulers

• fork: child is a copy; returns 0 in child, child PID in parent; memory is copied, not shared.
• n sequential forks → 2ⁿ processes, 2ⁿ − 1 children; prints after forks happen once per process; inside a loop, add per iteration.
• exec replaces the program; wait waits for a child; zombie = exited, not waited for; orphan = parent gone.
• Context switch = save + load PCB (overhead).
• Long-term (admission, degree of multiprogramming), short-term (CPU), medium-term (swapping).

CInterleaved GATE-style questions

Q1 · MCQ · 1 mark(s) — States

A process requests a disk read. It moves from Running to:

1. (A) Terminated
2. (B) Waiting
3. (C) New
4. (D) Ready

Q2 · MCQ · 1 mark(s) — Layout

A global variable int count = 0; is stored in the:

1. (A) heap
2. (B) PCB
3. (C) stack
4. (D) data segment

Q3 · NAT · 1 mark(s) — Fork

fork(); fork(); fork(); printf("hi"); How many times is hi printed?

Numerical answer: ________

Q4 · NAT · 2 mark(s) — Fork

if (fork() == 0) fork(); printf("y"); How many times is y printed?

Numerical answer: ________

Q5 · NAT · 2 mark(s) — Fork

for (i = 0; i < 2; i++) { if (fork() == 0) printf("c"); } How many c's are printed?

Numerical answer: ________

Q6 · MCQ · 1 mark(s) — Return value

In the parent process, fork() returns:

1. (A) the parent's own PID
2. (B) 0
3. (C) the child's PID
4. (D) −1 always

Q7 · MCQ · 1 mark(s) — Zombie

A child has exited but its parent has not called wait(). The child is a(n):

1. (A) zombie
2. (B) thread
3. (C) daemon
4. (D) orphan

Q8 · MSQ · 2 mark(s) — After fork

Immediately after a successful fork(), which are true?

1. (A) The child's fork() returned 0.
2. (B) A change to a global variable in the child is seen by the parent.
3. (C) Parent and child run the same code.
4. (D) Both continue from the statement after fork().