ALU 101 ALU Hardware Components

Question 1

What is the primary purpose of the accumulator register in an ALU?

Accepted Answer

To store the result of arithmetic and logic operations

Answer

The accumulator register temporarily stores the result of ALU operations before it is written to memory or another register.

Question 2

Which component of an ALU is responsible for selecting between arithmetic and logic operations?

Accepted Answer

Multiplexer

Answer

A multiplexer (MUX) selects between different operation outputs based on the opcode control lines fed to the ALU.

Question 3

What does a full adder circuit require compared to a half adder?

Accepted Answer

An additional carry-in input

Answer

A full adder has three inputs—two operand bits and a carry-in—allowing it to be chained for multi-bit addition.

Question 4

In a ripple-carry adder, what causes the main performance limitation?

Accepted Answer

Carry propagation delay through each stage

Answer

Each stage must wait for the carry-out of the previous stage, causing delays that ripple from the LSB to the MSB.

Question 5

What is the function of the status register (flags register) in an ALU?

Accepted Answer

To record condition outcomes such as zero, carry, and overflow

Answer

The status register holds flag bits that indicate the outcome of the last ALU operation, used by branch instructions.

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test