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.
That's a very interesting board! It came out in 1976 (four years before the 8087) and cost $499 assembled, equivalent to $2900 in current dollars, so it was expensive. It was really a decimal processor built from simple TTL parts, and had four microcoded instructions: add, subtract, multiply, and divide. Arithmetic used the 74LS181, the very popular ALU chip. (It did multiplication with repeated addition; there's no ROM with digit products, unless that was a later version.) The "small RAM" was very small by modern standards: four 4-bit registers that each held 16 digits. Each register was implemented with a 74S189 chip.
The microcode is available, so it would be a fun project to write a simulator that runs the microcode.
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.
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...
That's a very interesting board! It came out in 1976 (four years before the 8087) and cost $499 assembled, equivalent to $2900 in current dollars, so it was expensive. It was really a decimal processor built from simple TTL parts, and had four microcoded instructions: add, subtract, multiply, and divide. Arithmetic used the 74LS181, the very popular ALU chip. (It did multiplication with repeated addition; there's no ROM with digit products, unless that was a later version.) The "small RAM" was very small by modern standards: four 4-bit registers that each held 16 digits. Each register was implemented with a 74S189 chip.
The microcode is available, so it would be a fun project to write a simulator that runs the microcode.
Manual and schematics are here if anyone is looking for them: https://bitsavers.org/pdf/northstar/boards/North_Star_Floati...
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)
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...
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.
I guess he didn't pop up because the article is 6 years old.
https://news.ycombinator.com/item?id=23362673
I'm here now if anyone has questions. I can't be online all the time :-)
Re-post that comment top-level, so folks can see that the Big Name is now on stage. ;)