US What power cycling does
A power cycle means turning a device off, removing its power completely for a short time, then turning it back on. Power cycling is the most reliable way to clear a fault that a normal restart does not fix, which is why it is the first step in so much support advice for computers, routers, modems and cameras.
The difference is what stays powered. During a software restart the power supply keeps running, and parts such as network controllers, USB hubs and the embedded controller may never fully reset. When the power is removed, every component loses its state: memory is cleared, capacitors drain and each chip starts again from its power-on defaults. A controller that has locked up, a port that has stopped responding or a link stuck in a bad state usually recovers.
Power cycling does not change settings or delete files. Configuration lives in non-volatile storage, so a router, PC or switch comes back with the same set-up it had before.
Power cycle vs restart vs reset
These terms are often used loosely, but they reset different amounts of the system.
| Action | Power removed | Memory cleared | Hardware reset | Typical use |
|---|---|---|---|---|
| Restart (warm reboot) | No | Yes, by the operating system | Partly | Updates, software faults |
| Shut down and start | Standby rail stays on | Yes | Mostly; fast startup may skip some | End of day, moving equipment |
| Power cycle | Yes, fully | Yes | Yes | Frozen devices, network faults |
| Hard reset (reset line) | No | Yes | Processor and chipset | Hung system, watchdog recovery |
| Factory reset | Not required | Yes | Settings erased | Last resort, handing over a device |
On Windows, fast startup saves part of the system state to disk at shutdown, so a shutdown is not always a clean start. A restart, or removing power, avoids that.
How to power cycle a device safely
The method is the same for a PC, router, switch or camera. The care taken depends on whether the device is writing data at the time.
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Shut down cleanly first. If the device still responds, close applications and shut down from the operating system so that open files and caches are written to storage.
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Remove the power. Switch off at the wall or unplug the DC lead. For laptops and tablets, a long press of the power button often forces the power off.
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Wait. Leave it for around 10 to 30 seconds so that the capacitors in the power supply drain and every chip loses power.
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Restore power in order. For a network, start the modem first, then the router, then the switches and the devices behind them, so that each finds the one before it ready.
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Check it came back. Confirm the fault has cleared. If the same fault returns, power cycling has only hidden it.
Remote power cycling
When a computer is in a roadside cabinet, on a mast or in a vehicle, nobody is there to pull the plug. A remote power cycle does the same job over a network.
The simplest way is a switched PDU, a power strip whose outlets can be switched over the network, or a smart relay that cuts and restores the supply on command. More capable is out-of-band management, which reaches the computer through a separate controller that keeps working when the operating system has crashed. On x86 systems that is Intel vPro or IPMI on server boards; some of the NVIDIA Jetson computers we supply take an optional Allxon module for remote power cycling and serial console access. Our article on remote on and off control for industrial vision computers covers wake-on-LAN and scheduled start as well.
Watchdog timers and auto power-on
Industrial computers can also recover on their own, without anyone sending a command. Two firmware features do most of the work, and they are usually set in the UEFI firmware settings before the system is deployed.
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Watchdog timer. A hardware counter that the software must reset at regular intervals. If the application or operating system hangs and stops resetting it, the watchdog resets the computer. Timeouts are usually programmable, often from 1 to 255 seconds. Many of the box PCs, DIN-rail PCs and embedded boards we supply include one.
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Auto power-on after power loss. Also called AT mode, or a restore-on-AC-loss setting. The computer starts as soon as power returns, instead of waiting for someone to press the button. Some panel PCs and box PCs set this with an AT/ATX switch.
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Ignition control. On in-vehicle computers, power-on and shutdown follow the ignition key, with a delay so the system closes down cleanly.
Is power cycling bad for hardware?
An occasional power cycle does no harm. The risk comes from cutting power while data is being written. An SSD can lose data that is still in its cache, and a file system can be left inconsistent. Drives with power loss protection hold enough charge to finish those writes, and an industrial UPS gives the computer time to shut down cleanly when the supply fails.
Frequent cycling also causes repeated heating and cooling, which over years stresses solder joints. If a device needs power cycling every day, treat that as a fault to investigate rather than a routine.
Quick answers on power cycling
Power cycling: common questions
What does it mean to power cycle a device?
Turn it off, unplug it, wait, then turn it on. Removing power completely resets every component, which a restart alone may not do.
How do I power cycle a PC?
Shut down, switch off at the wall and wait. Leave it for around 30 seconds, then reconnect and start it. On a laptop, a long press of the power button forces it off if it has frozen.
Is power cycling the same as restarting?
No. A restart keeps the power supply running, so some hardware never fully resets. A power cycle removes power from everything.
How do I power cycle a router?
Unplug it, wait, then plug it back in. If there is a separate modem, unplug both, start the modem first and the router once the modem is online.
Does power cycling a router reset its settings?
No. Settings are kept in non-volatile memory. Only a factory reset, usually by holding a recessed reset button, erases them.
We set the watchdog, power-on behavior and remote management of every industrial PC we supply as standard, and validate them before the system ships. Tell us how the site is powered and how it will be reached, and we will set the system to recover on its own.