Northstar made an S-100 card which did FP math, using BCD arithmetic. It had a ucode ROM and a 4b (single digit) ALU, and a few small RAMs to hold the digits. If I remember correctly you could program it to select how many digits you wanted in your representation, up to 14 digits. It did everything one digit at a time, and it had a 256 byte ROM to carry out any digit*digit product in one cycle. For normalization no data was moved -- just the pointer to the appropriate digit was incremented or decremented.

https://s100computers.com/Hardware%20Folder/NorthStar/FP%20B...

Must…resist…clicking link… I’ve got a lot to today and this is like carefully crafted bait to tie me up for the next 4 hours. :-)

Closely related, 8 days ago, 138 points & 28 comments:

https://news.ycombinator.com/item?id=48519011 (about the 8087's adder)

• Jimmc414

  today at 2:32 PM

  That's a different article by the same author, Ken Shirriff

  https://www.righto.com/2020/05/die-analysis-of-8087-math-cop...

  https://www.righto.com/2026/06/intel-8087-adder-reverse-engi...

  • bell-cot

    today at 3:30 PM

    Yes - I was just trying to give things a "this is interesting, so upvote & discuss!" kick. In the absence of Ken popping up with good "Author here for your 8087 questions" comment.

    • elpocko

      today at 3:40 PM

      I guess he didn't pop up because the article is 6 years old.

      https://news.ycombinator.com/item?id=23362673

      • kens

        today at 3:52 PM

        I'm here now if anyone has questions. I can't be online all the time :-)

        • bell-cot

          today at 4:58 PM

          Re-post that comment top-level, so folks can see that the Big Name is now on stage. ;)