What is "floating-point unit"

n. (context computer hardware English) A microprocessor that performs floating-point arithmetic. In older models of computer the FPU was not integrated into the central processing unit, but rather as a coprocessor if included at all.

A floating-point unit (FPU, colloquially a math coprocessor) is a part of a computer system specially designed to carry out operations on floating point numbers. Typical operations are addition, subtraction, multiplication, division, square root, and bitshifting. Some systems (particularly older, microcode-based architectures) can also perform various transcendental functions such as exponential or trigonometric calculations, though in most modern processors these are done with software library routines.

In general purpose computer architectures, one or more FPUs may be integrated with the central processing unit; however many embedded processors do not have hardware support for floating-point operations.

When a CPU is executing a program that calls for a floating-point operation, there are three ways to carry it out:

• A floating-point unit emulator (a floating-point library)
• Add-on FPU
• Integrated FPU

Some systems implemented floating point via a coprocessor rather than as an integrated unit. This could be a single integrated circuit, an entire circuit board or a cabinet. Where floating-point calculation hardware has not been provided, floating point calculations are done in software, which takes more processor time but which avoids the cost of the extra hardware. For a particular computer architecture, the floating point unit instructions may be emulated by a library of software functions; this may permit the same object code to run on systems with or without floating point hardware. Emulation can be implemented on any of several levels: in the CPU as microcode (not a common practice), as an operating system function, or in user space code. When only integer functionality is available the CORDIC floating point emulation methods are most commonly used.

In most modern computer architectures, there is some division of floating-point operations from integer operations. This division varies significantly by architecture; some, like the Intel x86 have dedicated floating-point registers, while some take it as far as independent clocking schemes.

Floating-point operations are often pipelined. In earlier superscalar architectures without general out-of-order execution, floating-point operations were sometimes pipelined separately from integer operations. Since the early 1990s, many microprocessors for desktops and servers have more than one FPU.