COMPSYS

Question 1

What is the key difference between compilation and interpretation?

Answer 1

Compilation translates high-level code into machine code before execution; interpretation executes code line-by-line during runtime.

Question 2

What are two advantages of compilation?

Answer 2

Optimized machine code for faster execution and ability to run multiple times without recompiling.

Question 3

What are two advantages of interpretation?

Answer 3

Easier debugging and platform independence — no machine-specific compilation required.

Question 4

What is combined compilation and interpretation? Give an example.

Answer 4

First compile to an intermediate form (e.g., Java Bytecode), then interpret or JIT-compile it at runtime.

Question 5

What is a virtual machine (VM) in this context?

Answer 5

A software simulation of a CPU that runs programs independently of hardware; e.g., Java Virtual Machine (JVM).

Question 6

What does the JVM use to execute Java programs?

Answer 6

It uses compiled bytecode (.class files), interpreted or JIT-compiled during runtime.

Question 7

What is Just-In-Time (JIT) compilation?

Answer 7

JIT compiles bytecode into machine code during runtime to improve performance.

Question 8

What is the role of a stack in a stack machine?

Answer 8

Stack holds operands for computation and return addresses for subroutines.

Question 9

Why do stack machines use stacks instead of registers?

Answer 9

Simpler instruction set, smaller code, flexible operand management.

Question 10

What is Reverse Polish Notation (RPN) and why is it used?

Answer 10

Postfix notation where operators follow operands; eliminates parentheses, ideal for stack evaluation.

Question 11

How are subroutines implemented using stacks?

Answer 11

Push return address and local variables onto the stack at call; pop return address on return.

Question 12

What is the difference between unconditional and conditional jumps?

Answer 12

Unconditional jump always branches; conditional jump branches only if a condition is met.

Question 13

How does the Program Counter (PC) behave in stack machines like JVM?

Answer 13

PC points to the current instruction and steps through sequentially.

Question 14

Why is Java compiled to bytecode instead of directly to machine code?

Answer 14

Portability, security, and runtime optimization flexibility.

Question 15

List 3 key properties of the JVM architecture.

Answer 15

1. Stack-based 2. Typed instructions 3. Variable-length instructions

Question 16

Would you choose compilation, interpretation, or a hybrid for multi-device systems? Why?

Answer 16

Hybrid — compile to intermediate bytecode, interpret/JIT it; ensures portability and runtime optimization.

Question 17

For rapid bug fixing and testing, choose compilation or interpretation?

Answer 17

Interpretation — allows immediate testing without recompilation.

Question 18

How do pure interpreters and JIT compilers differ at runtime?

Answer 18

Pure interpreter executes line-by-line; JIT compiles chunks into machine code during execution.

Question 19

In a stack machine, why might evaluating a + (b * c) be faster than in a register machine?

Answer 19

Stack machines avoid register allocation overhead and have simpler decoding.

Question 20

When is a stack machine preferable despite being slower?

Answer 20

For simplicity, smaller hardware, easier implementation — common in embedded systems or VMs.

Question 21

Convert this RPN to Infix: 5 6 + 7 2 - ×

Answer 21

(5 + 6) × (7 - 2)

Question 22

Convert this RPN to Infix: a b + c d + ×

Answer 22

(a + b) × (c + d)

Question 23

Convert this RPN to Infix: 4 5 × 6 7 × +

Answer 23

(4 × 5) + (6 × 7)

Question 24

In RPN 2 3 + 5 *, what is the final stack result?

Answer 24

25

Question 25

In RPN 8 2 / 3 +, what is the final stack result?

Answer 25

7

Question 26

Given RPN: 3 4 5 × + 6 -, what is the Infix expression?

Answer 26

(3 + (4 × 5)) - 6

Question 27

Given Infix: (x + y) × (a - b), what is the equivalent RPN?

Answer 27

x y + a b - ×

Question 28

During evaluation of a b + c d + ×, what is on the stack after the first addition?

Answer 28

[a+b, c, d]

Question 29

True or False: In RPN, parentheses are necessary to indicate order of operations.

Answer 29

False — the order is inherently clear.

Question 30

Why are stack machines like JVM naturally suited to RPN?

Answer 30

Because operands are pushed and operations work directly on stack values, no precedence management needed.

Question 31

Imagine a new language today: compiled, interpreted, or JIT compiled?

Answer 31

JIT compiled — balances performance and portability for modern multicore/cloud environments.

Question 32

Why is the program counter simpler to manage in stack machines?

Answer 32

Instructions are executed sequentially with implied operand order, no dynamic dependency tracking.

Question 33

Design for minimal embedded device: stack or register architecture?

Answer 33

Stack-based architecture — simpler, cheaper, more compact code.

Question 34

Critique: 'Interpretation is always worse than compilation.'

Answer 34

False — interpretation is faster for initial testing, dynamic environments, and adaptable execution.