coprocessor notes in details by santosh_gowda_7. The is an actual processor with its own specialized instruction set. It can operate on data of the. With the processor and later, the coprocessor is integrated. It has its own instruction set, instructions are recognizable because of the F- in front. Architecture. Instruction set. Introduction. The Intel , announced in This was the first floating point Coprocessor for the line of Processors.

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However, dyadic operations such as FADD, FMUL, FCMP, and so on may either implicitly use the topmost st0 and st1, or may use st0 insrtuction with an explicit memory operand or register; the st0 register may thus be used as an accumulator i. The was initially conceived by Bill Pohlman, the engineering manager at Intel who oversaw the development of the chip.

The purpose of the was to speed up computations for floating-point arithmetic, such as additionsubtractionmultiplicationdivisionand square root. The binary encodings for all instructions begin with the bit patterndecimal 27, the same as the ASCII character ESC although in the higher order bits of a byte; similar instruction prefixes are also sometimes referred to as ” escape codes “.

This is especially applicable on superscalar x86 80887 Pentium of and later where these exchange instructions are optimized down to a zero clock penalty. It worked in tandem with the or and introduced about 60 new instructions.

There was a potential crash problem if the coprocessor instruction failed to decode to one that the coprocessor understood. Bruce Ravenel was assigned as architect, and John Palmer was hired to be co-architect and mathematician for the project.

Intel 8087

For an instruction with a memory operand, if the instruction called for the operand to be read, the would take the word of data read by the main CPU from the data bus. As a consequence of this design, the could only operate on operands taken either from memory or from its own registers, and any exchange of data between the and the or was only via RAM.


Starting with thethe later Intel processors did not use a separate floating point coprocessor; virtually all included it on the main processor die, with the significant exception of the SX which was a modified DX with the FPU disabled.

The Intelannounced inwas the first x87 floating-point coprocessor for the line of microprocessors.

It also computed transcendental functions such as exponentiallogarithmic or trigonometric calculations, and besides floating-point it could also operate on instduction binary and decimal integers.

The looked for instructions that commenced with the ” sequence and acted on them, immediately requesting DMA from the main CPU as necessary to access memory operands longer than one word 16 bitsthen immediately releasing bus control back to the main CPU. The handles infinity values by either affine closure or projective closure selected via the status register.

If an instruction with a memory operand called for that operand to be written, the would ignore the read word on the data bus and just copy the address, then request DMA and write the entire operand, in coprocessor same way that it would read the end of an extended operand.

The design initially met a cool reception in Santa Clara due to its aggressive design.

All models of the had a 40 pin DIP package and operated on 5 volts, consuming around 2. The was an advanced IC for its time, pushing the limits of period manufacturing technology.

8087 Numeric Data Processor

The and have two queue status signals which are connected to the coprocessor to allow it to synchronize with the CPU’s internal timing of execution of instructions from its prefetch queue. With affine closure, positive and negative infinities are treated as different values.

An important aspect of the from a historical coproceesor was that it became the basis for the IEEE floating-point standard.


In practice, there was the potential for program failure if the coprocessor issued a new instruction before the last one had completed. The was able to detect whether it was connected to an or an by monitoring the data bus during the reset cycle. Other Intel coprocessors were the, and the Intel microprocessors Intel x86 microprocessors Floating point Coprocessors.

The differed from subsequent Intel coprocessors in that it was directly connected to the address and data buses. The coprocessor did not hold up execution of the program until the coprocessor instruction was complete, and the program had to explicitly synchronize the two processors, as explained above in the ” Design and development ” section. From Wikipedia, the free encyclopedia. The was in fact a full blown DX chip with an extra pin.

With projective closure, infinity is treated as an unsigned representation for very small or very large numbers. This makes the x87 stack usable as seven freely addressable registers plus an accumulator. Archived from the original on 30 September Because the and prefetch queues are different sizes and have different management algorithms, the determines which type of CPU it is attached to by observing a certain CPU bus line when the system is reset, and the adjusts its internal instruction queue accordingly.

Intel – Wikipedia

Then two Ms, then the latter half three bits of the floating point opcode, followed by three Rs. The retained projective imstruction as an option, but the and subsequent floating point processors including the only supported affine closure. Thus, a system with an was capable of true parallel processing, performing one operation in the integer ALU of the main CPU while at the same time performing a floating-point operation in the coprocessor.