This might be the most difficult CPU to program.
The Intel i860 was useless for general operating systems. Context switches took ~2,000 cycles.
*You* controlled the floating point pipeline. But, if you’re a genius, it was one of the most powerful chips that existed.
Jan 20, 2026 18:34I can’t understate how crazy this was.
With modern chips, even raw assembly, you’re only requesting “vertical” microcode.
That is, the hardware handles decoding, scheduling and timing.
The i860 was horizontal (VLIW)...which is frankly insane to market to consumers.
If an ADD takes 3 cycles, you better push two more dummy instructions!
You basically had to write code where the input variable and the output variable on THE SAME LINE had nothing to do with each other.
Imagine: "pfadd R1, R2, R3"
R3 is the result from 3 cycles earlier!
The i860 never took off, but had some odd knock-on effects in the world of computing:
- Windows NT was originally designed for the i860
- Steve Job’s NeXT workstation “GPU” was actually just an i860 /w a Mach Kernel
- Silicon Graphics used bundles of i860s to viewport things like Jurassic Park (RealityEngine)
- If you’re in the supercomputing world, you likely use MPI. The difficulty of i860 synchronization indirectly led to the grandfather of MPI (Touchstone Delta)
