An 8-bit signed integer holds −128 to +127, one more negative value than positive. Where does the asymmetry come from?

D. From two's complement having only one zero, leaving one spare negative

256 patterns, one zero, and the spare goes to the negatives. Sign-magnitude wastes a pattern on −0 and gets a symmetric range; two's complement spends it on −128 instead. The consequence is real: negating −128 overflows, which is a genuine edge case in production code.