56 pointsby nand2mario6 hours ago4 comments
  • bsaul3 hours ago
    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.

    • aidos3 hours ago
      Not sure if it has a name but often there’s a trend of “one thing leads to another” related articles on the HN front page.

      Yesterday there was something similar that might have planted a seed in your mind like it did for other people.

      https://news.ycombinator.com/item?id=46735133

      • nand2mario2 hours ago
        Right. Or it could be frequency illusion. Once you become aware of something, it appears to be more frequent:

        https://en.wikipedia.org/wiki/Frequency_illusion

      • y42an hour ago
        or probably just some kind of preference/selection bias.

        You own a red Mercedes now and suddenly you see only red Mercedes' on the streets.

    • hahahahhaah2 hours ago
      The mind data-mines.
  • userbinator3 hours ago
    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.

    • st_goliath12 minutes ago
      Yes, one can only hope Ken Shirriff eventually happens to come across one of those models, but I guess they are probably very rare these days.

      Besides the multiplication, the 386 had quite a number of teething problems[1], including occasionally broken addressing modes, unrecoverable exceptions, virtual address resolution bugs around the 2G mark, etc...

      A while ago, there was also an article posted here that analyzed the inner workings of the Windows/386 loader[2]. Interestingly, Windows simply checks a pair of instruction (XBTS/IBTS) that early 386 steppings had, but was later removed, raising an invalid opcode exception instead.

      Raymond Chen also wrote a blog post describing a few workarounds that Windows 95 had implemented[3].

      [1] https://www.pcjs.org/documents/manuals/intel/80386/

      [2] https://virtuallyfun.com/2025/09/06/unauthorized-windows-386...

      [3] https://devblogs.microsoft.com/oldnewthing/20110112-00/?p=11...

  • rep_lodsb2 hours ago
    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?

    • csmantle2 hours ago
      > AI?

      Probably not; this point is well justified by both theory and practice. Supporting suitably larger operands is indeed what naturally comes following the increase of computation demands.

      One point I do differ from the author is that register width don't necessarily correlate with the size of address space. Even 8bit machines can address a large space by splitting apart the logical address and using multiple registers. Likewise, having a wide register does not imply the same address width.

    • an hour ago
      undefined
  • themafia4 hours ago
    Excellent work. Thank you! Your 486 FPGA project looks pretty neat too.