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.<p>The microcode is available, so it would be a fun project to write a simulator that runs the microcode.<p>Manual and schematics are here if anyone is looking for them: <a href="https://bitsavers.org/pdf/northstar/boards/North_Star_Floating_Point_Board_FPB-A_Rev_5_1978.pdf" rel="nofollow">https://bitsavers.org/pdf/northstar/boards/North_Star_Floati...</a>