80386 Multiplication and Division

Author here. Happy to discuss the technical details. The broader goal is to understand the 80386 microcode and hardware, and build an FPGA core around it, similar to what was already done for the 8086.

Is there a rational explanation on why there seems to be a HN article answering the weirdest questions i had in my mind just a few days ago ? Only yesterday i wondered how did CPU performed division. I didn't ask or type anything about it. It was just in my mind. And now this.

Are we part of a collective mind ? Do social networks algorithms shape society that deeply that we all end up having about the same random thoughts ?

This is really scary in a way.

No discussion of these instructions on the 386 would be complete without mentioning that early revisions had a bug in the 32-bit multiply: https://retrocomputing.stackexchange.com/questions/17803/int...

I wonder if anyone outside of Intel has discovered the actual bug in the circuitry yet.

> It would go on to run Windows 3.0, Windows 95, early Linux

That feels like a stretch :) Maybe it indeed ran on it, but Pentium was available when Windows 95 was released and it was probably far more likely to be sold along with such new Pentium multimedia machines, than someone getting it for their old 386. But Windows 3.11 was its exact match!

The 80186 and NEC Vxx chips - and of course also the 286 - could already do mul/div in one cycle per bit (+ some overhead for the microcode). What they didn't have was the early-out optimization.

The three-operand form of IMUL also already existed on those processors.

>This wasn't just an incremental upgrade—it was the foundation that would carry the PC architecture for decades to come.

AI?

Excellent work. Thank you! Your 486 FPGA project looks pretty neat too.