ALU 101 ALU Design and Architecture

Question 1

What distinguishes a combinational ALU from a sequential ALU?

Accepted Answer

A combinational ALU produces outputs purely from current inputs with no internal state

Answer

A combinational ALU is entirely built from combinational logic — outputs are a direct function of current inputs with no flip-flops storing state.

Question 2

In a multi-function ALU, what determines how many operation select lines are required?

Accepted Answer

The number of distinct operations, since n select lines support up to 2^n operations

Answer

With n select lines you can encode 2^n operation codes, so the number of operations supported dictates the minimum required select lines.

Question 3

What is the role of a Wallace tree in fast multiplier circuits within an ALU?

Accepted Answer

To reduce multiple partial products into two rows using carry-save adders for fast summation

Answer

A Wallace tree uses a network of carry-save adders to reduce n partial products into a sum and carry row, which a final adder then combines quickly.

Question 4

Which design technique allows an ALU to begin processing new operands before the previous result is complete?

Accepted Answer

Pipelining

Answer

Pipelining splits the ALU operation into stages so a new operation can enter stage 1 while the previous operation is still in later stages.

Question 5

What is meant by 'functional completeness' in the context of an ALU's logic unit?

Accepted Answer

The set of logic operations provided can implement any possible Boolean function

Answer

A functionally complete set (e.g., {NAND} alone) can implement any Boolean expression; an ALU's logic unit should include enough operations to compose any function.

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test

ALU 101 ALU Design and Architecture