If we consider a machine that uses 64 bits to represent a number.
If 1 bit is used for sign, "x" bits to represent mantissa and (63-x) to store the (biased) exponent in a manner similar to the IEEE representation.
I'm using this question to check my knowledge of IEEE. Can we say the largest positive number using this machine is: $\left ( 63-x \right )* 2^{2^{x}-1}$