January 19, 2026
Microcode, mega drama
Conditions in the Intel 8087 floating-point chip's microcode
Vintage math chip cracked open — comments spiral from awe to “were we duped”
TLDR: A deep dive reveals the Intel 8087’s microcode uses 49 internal checks to run math fast. Comments explode into debate over hidden “register tricks,” with the author fielding questions and fans daring each other to rebuild the chip in modern code — proving old silicon still stirs big feelings.
Intel’s 80s math sidekick, the 8087, just got its tiny brain decoded: 49 little “if this then that” checks inside secret microcode decide everything from “is it zero?” to “which way to round.” The author literally cracked one open and photographed the silicon maze, mapping 1,648 micro-steps that make trigonometry fly. But the real action? The comments. When kens dropped in with “Author here if anyone has questions…,” it turned into a live AMA. One reader, dboreham, confessed they “feel a little cheated,” after learning old chips may have done clever behind-the-scenes tricks like register renaming (a fancy term for shuffling where data lives). Cue a spicy skirmish: some cheered the idea that 70s chips were secretly smart, others rolled their eyes at the label, reminding everyone this is microcode (tiny internal instructions), not magic. Meanwhile, 0xsn3k threw down a dare: rebuild the whole thing in modern chip languages like Verilog. The crowd loved it, joking about stuffing π into a mini memory and whether the 8087’s double-stack life (one for numbers, one for micro-steps) makes it the original “stack on stack” flex. It’s silicon archaeology meets Reddit drama — and it’s glorious. Read more via the Opcode Collective.
Key Points
- •The Intel 8087 implements complex math functions via internal microcode, using 49 conditional tests within its algorithms.
- •Die-level analysis shows a datapath for 80-bit floating-point operations, a constant ROM with values like π, and eight stack-arranged registers.
- •The microcode ROM contains 1648 16-bit micro-instructions that perform operations such as move, add, and shift.
- •A microcode engine generates an 11-bit micro-address and supports conditional jumps, subroutine calls, and returns, guided by Instruction Decode PLA and Jump PLA.
- •Six 11-bit registers form a microcode stack for up to six subroutine levels; bus and control circuitry manage interactions with the 8086 and system.