ALU scalability: Evaluate the statement: “Arithmetic logic unit (ALU) slices cannot be cascaded to operate on more than four bits.”

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Solve this multiple-choice question and choose the correct option.

Accepted Answer

Introduction / Context:Classic CPUs and many TTL/MSI designs build wide datapaths by cascading smaller ALU slices (e.g., 4-bit units) with carry connections. The 74181 is a well-known historical example used to assemble 8-, 12-, or 16-bit ALUs. Given Data / Assumptions: ALU “slice” width is often 1, 2, or 4 bits. Cascading uses carry chains or look-ahead logic. Concept / Approach:To scale width, chain Cout of a lower slice into Cin of the next. Performance can be improved with carry look-ahead, carry-skip, or carry-select techniques. Therefore, not only is cascading possible, it is a standard approach in modular ALU design. Step-by-Step Solution: Identify claim: “cannot be cascaded.”Recall standard practice: 4-bit slices commonly chained.Conclude claim contradicts established design patterns → “Incorrect.” Verification / Alternative check:Datasheets and textbooks show ripple and look-ahead chains of 74181 slices forming wider ALUs. Why Other Options Are Wrong: Correct / serial-only: Both incorrect; parallel slice cascading is common.Ambiguous without timing: Timing affects speed, not possibility. Common Pitfalls:Equating four-bit demo circuits with inherent architectural limits. Final Answer:Incorrect

ALU scalability: Evaluate the statement: “Arithmetic logic unit (ALU) slices cannot be cascaded to operate on more than four bits.”

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