firm error
A type of error where a signal or datum becomes wrong and remains wrong until the equipment is power-cycled, but does not physically damage the equipment's hardware.
firm error: stuck data that survives until restart
A firm error is a fault state in which a system's signal or data value becomes corrupted and persists in that state until the device is powered down and restarted. Unlike a hard error, which reflects actual physical damage to components, a firm error leaves the hardware intact and functional. The equipment itself has not broken, but its output or internal state has locked into a wrong value.
Firm errors typically arise from software glitches, memory corruption, sensor calibration loss, or transient electrical disturbances that the system fails to correct or clear on its own. A sensor reading may stick at an incorrect value; a logic circuit may latch into an erroneous state; a buffer may hold corrupted data that subsequent operations read and propagate. The system has no self-healing mechanism and no automatic error recovery protocol active enough to purge the fault.
Firm error versus hard error
The distinction matters operationally. A hard error, such as a broken transistor or failed capacitor, requires replacement or repair of physical components. A firm error requires only a power cycle, unplugging the equipment or toggling its main breaker to reset all registers and memory to their default states. This is why technicians routinely power-cycle devices as a first troubleshooting step before assuming component failure.
Firm errors are common in control systems, programmable logic controllers (PLCs), data acquisition equipment, and industrial computers. They occur more frequently in devices with limited error-detection and error-correction (EDAC) circuitry, or in systems running firmware without watchdog timers or automatic fault clearing routines. Equipment operating in electrically noisy environments, with poor grounding or inadequate surge protection, experiences firm errors at higher rates.
The term distinguishes this class of fault from transient errors, which correct themselves automatically, and from hard errors, which require component replacement. In maintenance records and diagnostic procedures, identifying a firm error versus hardware failure directs the response: restart the system, or order a replacement module. This classification has been standard in industrial electronics and telecommunications since the emergence of solid-state systems in the 1970s and 1980s.