ALU 101 Carry and Overflow

Question 1

What is a carry bit in binary addition?

Accepted Answer

A bit propagated to the next higher position when the sum exceeds 1

Answer

A carry bit is generated when the sum of two bits (plus any incoming carry) is 2 or 3, and it propagates to the next higher bit position.

Question 2

A half adder computes which two outputs?

Accepted Answer

Sum and Carry

Answer

A half adder computes the Sum (using XOR) and the Carry-out (using AND) for two single-bit inputs.

Question 3

What additional input does a full adder have compared to a half adder?

Accepted Answer

Carry-in

Answer

A full adder accepts a Carry-in input in addition to the two data bits, allowing chaining of multiple adders.

Question 4

Adding 0111 + 0001 in 4-bit unsigned binary produces what result and carry?

Accepted Answer

Result=1000, Carry=0

Answer

0111 + 0001 = 1000 in 4-bit binary; no carry is generated out of the 4-bit boundary.

Question 5

In a ripple carry adder, why does carry propagation slow down the circuit?

Accepted Answer

Each bit's carry must wait for the previous bit's carry to settle

Answer

In a ripple carry adder, each stage must wait for the carry from the previous stage, so delay accumulates through all stages.

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test