Tan,

Floating point numbers are of two types, standard and double precision.

Standard uses 4 bytes and can represent from about 10^38 to 10^-38 and a with a precision of about 6-7 digits. The value is stored in 2 parts, i.e. mantissa and exponent. 3 bytes are used to store mantissa and 1 is used to store exponent.

Double precision requires 8 bytes and can store approx 10^308 to 10^-308 with a precision of 15 digits.

More details can be found in a good text book about programming, e.g C or VB.

Regards

IA