Here is an addition problem using 4-bit operands:
1111 0111 1001 0000 Overflow happened
Two four-bit numbers are added,
but the sum does not fit in four bits.
If we were using five bits the sum would be
But with four bits there is no room
for the left-most "1".
Because the carry out from the most significant
column of the sum is "1",
the 4-bit result is not valid.
The column is called the most significant column
because it corresponds to the highest power of two.
The bits in the leftmost columns are called the most significant bits
or the high-order bits.
The electronic circuits of a processor can easily detect overflow of unsigned binary addition by checking if the carry-out of the leftmost column is a zero or a one. A program might branch to an error handling routine when overflow is detected.
Add these unsigned numbers, represented in eight bits. Determine if overflow occurs.
0010 1100 0101 0101