Given n bits, use the most significant (leftmost) bit for the sign("1" means negative),
and the remaining n-1 bits to represent the magnitude.
Examples (assuming 8 bits):
33 is represented by 0010 0001
-33 is represented by 1010 0001
Remarks
with 16 bits, -33 is represented by
1000 0000 0010 0001
Given n bits, there are 2^{n-1} - 1 possible positive number representations
2^{n-1} - 1 possible negative number representations
and 2 zero representations (!)