IBM Floating Point Architecture - IEEE 754 On IBM Mainframes

IEEE 754 On IBM Mainframes

Starting with the S/390 G5 in 1998, IBM mainframes have also included IEEE binary floating-point units which conform to the IEEE 754 Standard for Floating-Point Arithmetic. IEEE decimal floating-point was added to IBM System z9 GA2 in 2007 using millicode and in 2008 to the IBM System z10 in hardware.

Modern IBM mainframes support three floating-point radices with 3 hexadecimal (HFP) formats, 3 binary (BFP) formats, and 3 decimal (DFP) formats. There are two floating-point units per core; one supporting HFP and BFP, and one supporting DFP; note there is one register file, FPRs, which holds all 3 formats.