The adder at the heart of Intel's 8087 floating-point chip
Key takeaways
- In 1980, Intel released the Intel 8087 floating-point coprocessor, a chip that could make math up to 100 times faster.
- The photo below shows the 8087 die under a microscope.
In 1980, Intel released the Intel 8087 floating-point coprocessor, a chip that could make math up to 100 times faster. As well as arithmetic and square roots, the 8087 computed transcendental functions including tangent, exponentiation, and logarithms. But it all depended on a 69-bit adder: "The arithmetic heart of the floating-point execution unit is centered about a nanomachine comprised of the adder and its related registers, shifters and control circuitry," as the patent describes it. In this article, I explain the circuitry of this adder.
The photo below shows the 8087 die under a microscope. Around the edges of the die, hair-thin bond wires connect the chip to its 40 external pins. The complex patterns on the die are formed by its metal wiring, as well as the polysilicon and silicon underneath. At the top of the chip, the Bus Interface Unit connects to the rest of the system: coordinating with the main 8086 processor and memory. The chip's instructions are defined by the large microcode ROM in the middle.