80386 Multiplication and Division

Post by ack_complete » Sat, Jan 24, 2026, 6:42 PM UTC

rep_lodsb wrote: post #8

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?

The timeline for fast multiplies is also a bit off, IMUL was already 4c latency / 1c throughput on the Pentium Pro (1995) and Pentium II (1997). Pretty sure IMUL was also only a few cycles on the AMD K6 (1997). Though Intel slowed it back down again in the Pentium 4, until they reverted back to the P6 architecture in the Pentium M.

Post by TacticalCoder » Sat, Jan 24, 2026, 7:50 PM UTC

Aardwolf wrote: post #19

> 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!

> 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.

I was definitely running Linux on a 486. I even had a big bulky laptop back then but I don't remember what CPU it had: I was running Linux on it too. And my 486 was sharing it's (dial-up, 28.8 or 33.6) Internet connection to the laptop using the PLIP protocol (IP over a parallel cable): I set that up and my brother and I were discovering the Web at the same time. Fun memories.

The jump was not 386 to Pentium. The 486 had its glory days.

Re: 80386 Multiplication and Division

Re: 80386 Multiplication and Division