ALU 101 Carry and Overflow 3

Question 1

What is the purpose of the carry save adder (CSA)?

Accepted Answer

To speed up multi-operand addition by deferring carry propagation

Answer

A carry save adder speeds up adding three or more numbers by saving carries for a final fast adder rather than propagating them immediately.

Question 2

In binary subtraction A − B using two's complement, the operation becomes:

Accepted Answer

A + (−B) = A + two's complement of B

Answer

Subtraction A − B is performed as A plus the two's complement of B, allowing the same adder circuit to handle subtraction.

Question 3

What happens to the carry flag when 1111 + 0001 is computed in 4-bit unsigned arithmetic?

Accepted Answer

Carry = 1, result = 0000

Answer

1111 + 0001 = 10000, which is 5 bits; the 4-bit result is 0000 and the carry-out flag is set to 1.

Question 4

Which flag in the ALU status register indicates the result of an operation is zero?

Accepted Answer

Zero flag (Z)

Answer

The zero flag (Z) is set by the ALU when the result of an operation is exactly zero.

Question 5

Why is the carry lookahead adder faster than the ripple carry adder?

Accepted Answer

It computes all carry bits in parallel rather than sequentially

Answer

The carry lookahead adder generates all carry bits simultaneously using propagate and generate logic, eliminating sequential carry ripple delay.

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test