Before the formats of floating point numbers have been standardized in IEEE 754 in 1985, different vendors had used many different floating point formats, some of them listed on the Data Format and Conversion Information for Heritage Data at the National Space Science Data Center page.
Most — but not all — of those formats define a "double precision" format, initially for the sake of the FORTRAN
DOUBLE PRECISION type. It is my understanding that in most configurations, a computer either didn't have a FPU at all, and all floating point operations were emulated using integer instructions in the CPU, or the FPU had hardware support for both formats; in both cases the performance ratio between single and double precision computations being in the low single digits.
My questions are:
- on the platforms for which the double precision format is not defined (e.g. CDC), was FORTRAN lacking the
- was there a Western1) computer for which the double precision format was defined, but whose FPU only implemented single precision, necessitating software emulation of the double precision f. p. arithmetic (thanks to lvd), using single precision f. p. instructions whenever possible, of course, but still resulting in a substantial performance degradation for double precision computations?
1) BESM-6 suffered from exactly that; its software-emulated double precision was at least 10x slower than the native floating point.