In practice most machines use at least 32 bits to store real numbers.
Many systems now use the IEEE Standard representation: for 32-bit
numbers this gives a precision of just over 7 decimal digits and allows a
number range from around 10^{-38} to just over 10^{+38}. This can be
something of a limitation because there are many types of calculation,
especially in physics and astronomy, which lead to numbers in excess of
10^{40}. Some computers designed expressly for scientific work,
sometimes called ``super-computers", allocate 64 bits for real numbers so
that the numerical precision is much larger; the range is often larger as
well. On such machines it is rarely necessary to use the double
precision type.