Don't waste money on a math coprocessor they said

Original Article ↗ Hacker News Discussion ↗

Early PC “math coprocessors” were once expensive add‑ons that dramatically accelerated CAD, 3D rendering, games, and scientific software, and their quirks could even determine whether titles like Quake or BattleTech ran at all. Commenters recount how floating‑point units evolved from optional chips (8087/287/387, Weitek, 68881/2) into standard CPU features, along with oddities like buggy early 386s, OS/2 instability, and marketing-driven parts such as the 486SX/487. The exchange also draws parallels to today’s hardware landscape, comparing historical FPU integration to modern GPU and accelerator trends and noting recurring cycles of specialization and reintegration in system design.

Evolution of Coprocessors, GPUs, and Integration

  • Early FPUs (x87, Weitek, m68881/2, etc.) are likened to “the GPUs of their day” – separate chips that later became integrated.
  • Many note that current CPUs are effectively SoCs with CPU, GPU, and other units on one package; true high‑end GPUs remain discrete due to die size, heat, and cooling constraints.
  • Apple’s M‑series and high‑end APUs (e.g., Ryzen G) are cited as strong integrated CPU/GPU examples, though not top performance per watt vs desktop/server GPUs.
  • Newer server parts (e.g., Intel Xeon Max with on‑package HBM and matrix/tensor instructions) are mentioned as another form of integration.
  • Thread links this to a “wheel of reincarnation” where functions oscillate between discrete cards and integration (Wi‑Fi, BT, audio, etc.).

Games, Software, and FPU Impact

  • Many share experiences where FPUs transformed workloads: CAD (AutoCAD), 3D rendering (3D Studio, POV-Ray), financial/insurance calculations, and niche games (Quake, El‑Fish, Falcon, Dune II).
  • Quake is highlighted as heavily optimized for Pentium’s FPU quirks and superscalar design; 486 systems often struggled despite similar MHz.
  • Some DOS games detected a coprocessor and ran noticeably faster, but most used integer math and gained little.
  • Simulations and raytracing on 286/386 without FPU are recalled as multi‑hour or overnight jobs, dropping to minutes with a math coprocessor.

The BattleTech / OS/2 Mystery

  • Several readers expected an explanation for why BattleTech only ran with a coprocessor; consensus is that the root cause remains unclear.
  • Hypotheses include:
    • Early or slightly defective 386 CPU behavior.
    • PS/2 hardware quirks and partial IBM‑PC compatibility.
    • Bugs in early OS/2 2.0 betas, especially around virtual 8086 mode and floating‑point emulation/interrupts.
    • Physical issues like marginal connections or dust, though the author reports cleaning and even replacing the CPU.

CPU/FPU Product History and Clarifications

  • Thread corrects common confusion between:
    • True coprocessors (8087–80387) vs. 486SX/DX and the 487, which was effectively a full replacement CPU.
  • Mentions third‑party FPUs (Cyrix, IIT, Weitek) and odd combos like mismatched CPU/FPU clock speeds with “Turbo” buttons.

Nostalgia and Broader Reflections

  • Strong nostalgia around installing FPUs, overclocking 386/486 systems, tuning jumpers, and watching multi‑floppy installs and slow raytraces.
  • Some reflect on how modern games now approach the fidelity of 1990s box art, and how dramatic capability jumps once came from single add‑in cards or coprocessor upgrades.