Ask HN: Who's still keeping a DOS machine up because the business depends on it?

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Across industries from laboratories and factories to railways, nuclear plants and small retailers, many critical systems still run on DOS-era or similarly antiquated hardware and operating systems. Commenters describe why these setups persist—hardware lock‑in, regulatory certification, high migration costs, and the reliability of well‑understood systems—alongside the growing fragility of decades‑old components. Emulation, virtualization, and now AI‑assisted code migration are emerging as workarounds, but organizations often defer change until failure or regulation forces a costly, risky replacement.

Prevalence of Legacy DOS and Other Old Systems

  • Many comments describe active use of DOS-era or similar systems in labs, factories, CNC machines, wave soldering equipment, radio programming, pick‑and‑place machines, gas stations, lumberyards, POS/accounting, and medical analyzers.
  • Non‑DOS but comparable cases include OS/2, SCO UNIX, Windows 3.11/95/98/NT/XP, VAX/VMS, old mainframes, and even C64-controlled equipment.
  • Some setups are still directly on hardware; many are now run via VMs or emulators.

Why Old Systems Persist

  • Replacement is expensive, risky, or requires recertification (e.g., nuclear plants, flight simulators, regulated industrial/medical gear).
  • Tooling is tied to obscure hardware (ISA cards, GPIB, parallel/serial, dongles, proprietary buses).
  • Software does its job reliably and operators are used to it; downtime costs or training burden outweigh benefits of modernization.
  • Vendors and original devs are gone, and source code is often unavailable.

Hardware & Interface Constraints

  • ISA, GPIB, parallel ports, and legacy serial protocols are central blockers; spare parts are scavenged from eBay or museums.
  • Attempts to bridge to modern systems include ISA‑over‑USB projects and special laptops/docks with real serial/parallel ports, but latency and timing are concerns.
  • Some systems use bespoke IO cards or instrument connections that are hard to replicate.

Emulation, Virtualization, and Integration

  • Solutions include DOSBox, DOSEMU, vDos, FreeDOS, QEMU, Linux+Samba+CUPS gateways, and full VMs carrying whole legacy stacks.
  • Integration patterns often encapsulate old boxes behind Linux/Windows intermediaries, VLANs, and file/print translation layers.
  • Airgapping and network segregation are emphasized to satisfy security audits while avoiding changes to legacy machines.

Proposed Tooling and Market Skepticism

  • One idea: a DOS runtime/emulator with interrupt/I/O hooks to log all calls, mirror .DBF activity into modern databases, and map legacy IO to USB.
  • Responses see this as a tiny, highly customized, low‑budget niche, though technically interesting.

AI and Long‑Lived Software

  • Some report using AI to port QuickBASIC DOS apps to modern languages as a stopgap.
  • Others argue AI could now rebuild many old apps cheaply, but hardware lock‑in, verification, and regulatory burdens remain major obstacles.
  • Suggestions for future‑proof systems include open source, popular languages, strict specs, hardware‑agnostic OSes, and self‑contained build processes.