EMZETT.Cold boot, warm boot and fast boot
In short: A cold boot is a start from the powered-off state, a warm boot a restart without cutting power, and fast boot skips checks or restores a saved state to be quicker.
In more detail: The terms describe how much of the startup process is really run and how completely the hardware is reinitialized.
In Depth
| Cold boot | Warm boot | Fast boot / fast startup | |
|---|---|---|---|
| Starting state | off, powerless | running | shut down but state saved |
| Trigger | power button, mains switch | restart, Ctrl+Alt+Del | switching on after “Shut down” |
| Power cut? | yes | no | no/partly |
| Full POST | yes | often shortened | strongly shortened or skipped |
| RAM contents | lost | overwritten anew | not kept, but hibernation file loaded |
| Duration | longest | shorter | shortest |
- Warm boot resets processor and operating system, the hardware stays powered. Formerly with Ctrl+Alt+Del, today “Restart”.
- Fast boot (UEFI): The firmware skips device checks and USB initialization. Handy, but you hardly reach the UEFI menu anymore.
- Windows fast startup: “Shut down” saves the kernel state like hibernation. The next start loads the image. Only a real restart performs a complete start.
- Problems with fast startup: Updates take effect late, drivers hang, dual-boot systems and drives stay “locked”, network cards do not restart. Remedy: switch off fast startup in power options or use restart instead of shut down.
- Cold boot attack: An attack that reads keys from RAM while it still briefly retains data after switch-off (cooling extends that). Countermeasures: RAM wipe at startup, soldered memory, TPM protection.
- Mnemonic: Cold = fully off. Warm = off and on again by software. Fast = restore state.
See also: Boot process of a Windows 11 computer, POST (power-on self-test), BitLocker