A double-precision datum is an approximation of a real number. The double-precision data type, DOUBLE PRECISION, which has the synonym, REAL*8, holds one double-precision datum.
The default size for DOUBLE PRECISION with no size specified is 8 bytes.
A DOUBLE PRECISION element has a sign bit, an 11-bit exponent, and a 52-bit fraction. These DOUBLE PRECISION elements in f77 conform to the IEEE standard for double-precision floating-point data. The layout is shown in Appendix C, Data Representations .