ALU 101 ALU Design and Architecture 2

Question 1

What is the primary advantage of a carry-save adder (CSA) when multiplying large numbers?

Accepted Answer

It defers carry propagation until the final addition, speeding up partial product reduction

Answer

A CSA produces a sum and carry output without propagating carry through all bits, allowing fast tree-based reduction of many partial products.

Question 2

What does the 'critical path' of an ALU determine?

Accepted Answer

The maximum clock frequency, set by the longest combinational delay through the circuit

Answer

The critical path is the longest gate-delay path in the ALU; the clock period must be long enough for signals to traverse it, setting the maximum frequency.

Question 3

How does Booth's algorithm improve binary multiplication in an ALU?

Accepted Answer

It reduces the number of partial products by recoding the multiplier to include -1 terms

Answer

Booth's algorithm recodes consecutive 1s in the multiplier into a subtract followed by an add, reducing the number of partial products and speeding up multiplication.

Question 4

In a superscalar processor, what is required for two ALU operations to execute in parallel?

Accepted Answer

They must have no data dependencies between them

Answer

Parallel execution requires that neither operation reads a register the other is writing, i.e., no RAW, WAR, or WAW hazards exist.

Question 5

What is the purpose of operand forwarding (bypassing) in a pipelined ALU datapath?

Accepted Answer

To route a computed result directly to the next instruction's input without waiting for register writeback

Answer

Forwarding paths allow a result in the EX or MEM stage to feed directly into the ALU input for a dependent instruction, reducing stall cycles.

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test

ALU 101 - Arithmetic Logic Unit 101 Exam Practice Test

ALU 101 ALU Design and Architecture 2