Air gaps protect systems where compromise would be catastrophic: industrial control networks, classified systems, backup vaults, and signing or key-management infrastructure. Data crosses the gap only through controlled means — scanned removable media, one-way transfer devices, or scheduled physical processes.
Key points
Whole-boundary designAccount for maintenance laptops, vendor remote access, USB devices, firmware updates, telemetry paths, and administrative jump hosts — the gap fails at its convenience exceptions.
Enforced one-way transferData diodes and scheduled, scanned media exchanges preserve isolation better than ad hoc file copies.
Important limitationAir gaps raise cost and reduce monitoring, patching, and response capability — isolated systems can drift unpatched and unaudited. They have also been bridged historically via removable media and maintenance paths, so an air gap reduces exposure; it does not eliminate it.