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 1040. 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.