Post

Ken Shirriff
@righto.com

In 1980, Intel announced the 8087 Math Coprocessor, a chip that made floating-point 100 times faster. I opened up the chip, took photos of the silicon structures, and analyzed its circuitry. It's a very complex chip for its time. Let's take a look inside...

34 reposts127 likes

Ken Shirriff
@righto.com

Unlike most processors, the 8087 organizes its registers into a "stack", pushing numbers onto the top of the stack and popping them off. Here's a close-up of the eight registers, organized in a grid of cells. Each register holds an 80-bit number, so the registers are very tall.

L Break Into Program
@breakintoprogram.co.uk

It sounds like you are describing Reverse Polish Notation there. I wonder if the engineers took inspiration from their HP scientific calculators? (I had one in college, given to me by a friend of the family. Fellow students would only borrow it once, more fool them).

Ken Shirriff
@righto.com

Each bit is stored in a "static RAM" cell, consisting of two inverters in a loop. This circuit has two stable states, holding a 0 or a 1. The implementation is complicated: silicon with polysilicon lines on top to make transistors. Horizontal metal wires connect everything.

Ken Shirriff
@righto.com

This diagram, based on the 8087 patent, shows the implementation of the stack. You saw the registers (yellow) earlier. This photo shows the three-bit circuitry that controls the stack (purple, green, and blue). The schematic shows one bit in detail.

Ken Shirriff
@righto.com

Intel was hesitant to produce the 8087 chip, considering it complex, risky, and with an unknown market. Intel's Israel site took on the project; the die is marked "i/IL". The chip was a highly profitable success. Now, almost all computers use floating-point systems based on the 8087.

aka_pugs
@akapugs.bsky.social

Gustafson's book has great background on how the 8087 became the basis of IEEE 754 floating point. Everyone should read the book to learn how messed up IEEE 754 is, but how much better it was than its predecessors. And posits are so cool. www.routledge.com/Every-Bit-Co...

routledge.comEvery Bit Counts: Posit ComputingWritten by one of the foremost experts in high-performance computing and the inventor of Gustafson’s law, Every Bit Counts: Posit Computing explains the foundations of a new way for computers to calcu...
Edward Vogel
@mathartforall.bsky.social

I remember working on a defense project at a little shop in San Diego and the dude that designed an FPGA that leveraged IEEE 754 and my boss were having a freak out at it miscalculating something.

Edward Vogel
@mathartforall.bsky.social

A guy at the UCSD Sci/Tech library told me about a similar issue - chit chat at the copy machine...mentioned it to FPGA dude and boss. 1st reaction- you're a technician, shut up. Ten minutes later - tell us more. I think it turned out to be a typo when we finally got the up to date doc.