integer into the FPU, while the latter writes a FPU value as a 80-bit integer value into the memory. Inside of the FPU, the values are stored as normal x87 extended-precision floats. Unlike the integer-facing versions, the two instructions remain available in long mode. The 80-bit format is divided into the following: There is a special "indefinite" value encoded as FFFFC000000000000000h. Application Binary-coded decimal (BCD) numbers are used for storing decimal numbers, especially in financial software. The opcodes mentioned above give the x86 rudimentary BCD support. Alternatives Adding BCD numbers using these opcodes is a complex task, and requires many instructions to add even modest numbers. It can also require a large amount of memory. If only doing integer calculations, then all integer calculations are exact, so the radix of the number representation is not important for accuracy. On an x86 processor, calculations with binary numbers are usually a lot faster than the same calculations with BCD numbers. See also Bit Manipulation Instruction Sets References X86 instructions