VMS Help FORTRAN, Data, Types, REAL  *Conan The Librarian (sorry for the slow response - running on an old VAX)

  Real and complex numbers are floating-point representations.

  The exponent for REAL*4 and REAL*8 (D_floating) formats is stored
  in binary excess 128 notation.  Binary exponents from -127 to 127
  are represented by the binary equivalents of 1 through 255.

  The exponent for the REAL*8 (G_floating) format is stored in binary
  excess 1024 notation.  The exponent for the REAL*16 format is
  stored in binary excess 16384 notation.  In REAL*8 (G_floating)
  format, binary exponent from -1023 to 1023 are represented by the
  binary equivalents of 1 through 2047.  In REAL*16 format, binary
  exponents from -16383 to 16383 are represented by the binary
  equivalents of 1 through 32767.

  For each floating-point format, fractions are represented in
  sign-magnitude notation, with the binary radix point to the left of
  the most significant bit.  Fractions are assumed to be normalized,
  and therefore the most significant bit is not stored.  This bit is
  assumed to be 1 unless the exponent is 0., in which case the value
  represented is either zero or is a reserved operand.

  REAL*4 (F_floating) numbers occupy four contiguous bytes and the
  precision is approximately one part in 2**23, that is, typically 7
  decimal digits.

  REAL*8 (D_floating) numbers occupy eight contiguous bytes and the
  precision is approximately one part in 2**55, that is, typically 16
  decimal digits.

  REAL*8 (G_floating) numbers occupy eight contiguous bytes the
  precision is approximately one part in 2**52, that is, typically 15
  decimal digits.

  REAL*16 (H_floating) numbers occupy sixteen contiguous bytes and
  the precision is approximately 2**112, that is, typically 33
  decimal digits.