- Reverse-engineering the multiplication algorithm in the Intel 8086 processor (righto.com)
While programmers today take multiplication for granted, most microprocessors in the 1970s could only add and subtract — multiplication required a slow and tedious loop implemented in assembly code. One of the nice features of the Intel 8086 processor (1978) was that it provided machine instructions for multiplication, able to multiply 8-bit or 16-bit numbers with a single instruction. Internally, the 8086 still performed a loop, but the loop was implemented in microcode: faster and transparent to the programmer. Even so, multiplication was a slow operation, about 24 to 30 times slower than addition.