Intel's 8087 made floating-point addition nearly 100 times faster
The Intel 8087 chip: floating-point addition and subtraction
In 1980, Intel's 8087 coprocessor sped up floating-point addition by almost 100x over the 8086. Ken Shirriff decaps a chip, traces its microcode, and walks through the 69-bit adder, barrel shifter, and exponent logic that align binary points, normalize results, and handle infinities, NaNs, and signed zeros.
The 8087 provided a spectacular speed improvement over the 8086 processor, speeding up addition by a factor of almost 100, and complicated operations by even more.
- WalterBright
I always thought the 8087 was way cool, but it never really caught on. Early versions of Win32 did not save the 8087 registers on a context switch. I called up some people at Microsoft to please not destroy the 8087, and they relented and preserved the registers.
I've always been proud to support the 8087 with my compilers, and am baffled why the numerics people ignore it.
- dsign
Kind of shocking that a 1980 chip could do 80 bits floating points. It makes me a little mad at all of those microcontrollers from this year, 46 years later that ship without floating point support or, at best, 32 bits, but they do come with a "secure island" and a radio capable to ring ET.
- kens
Author here with another 8087 article. What part of the 8087 should I look at next?
- kar1181
Gosh thank goodness for Ken, a beacon of light in a sea of slop. For all these years, and countless hours of posts and videos, thank you.