ALU 101 Control Signals and Flags

Question 1

What does the Carry flag (CF) indicate after an ALU addition operation?

Accepted Answer

A carry-out occurred beyond the MSB of the result

Answer

The result is negative

Answer

The result equals zero

Answer

An arithmetic overflow occurred in signed arithmetic

Question 2

Which flag is set when the result of an ALU operation is exactly zero?

Accepted Answer

Zero flag

Answer

Sign flag

Answer

Overflow flag

Answer

Parity flag

Question 3

What is the purpose of the Overflow flag (OF) in ALU operations?

Accepted Answer

To signal that a signed arithmetic result exceeded the representable range

Answer

To indicate unsigned carry-out

Answer

To mark a parity error

Answer

To indicate a divide-by-zero condition

Question 4

What do ALU control lines (operation select lines) determine?

Accepted Answer

Which arithmetic or logic operation the ALU performs on its inputs

Answer

The clock frequency

Answer

The bit width of the operands

Answer

The number of pipeline stages

Question 5

The Sign flag (SF) in x86 architecture mirrors which bit of the ALU result?

Accepted Answer

The MSB (most significant bit)

Answer

The LSB (bit 0)

Answer

The second MSB

Answer

The carry-out bit

Question 6

What does the Parity flag indicate after an ALU result is computed?

Accepted Answer

Whether the number of set bits in the low byte of the result is even

Answer

Whether the result is even or odd as a whole number

Answer

Whether a carry was generated

Answer

Whether the result has an overflow