warm boot / cold boot
expressionIT support
Restarting without cutting power versus from full power-off - the cold boot clears states the warm one preserves.
Why 'turn it off and on again' sometimes fixes what 'restart' did not.
A cold boot is a full power cycle; a warm boot is a restart that leaves power applied. The difference is not pedantry, because it determines what state survives, and the state that survives is exactly what you may be trying to clear.
Hardware is the usual reason it matters. A network interface, storage controller or peripheral that has entered a confused condition may be reset by its own firmware on a warm restart and only genuinely reinitialized when power is removed, so a device that keeps misbehaving across reboots often needs the power actually cut. Remote administration typically offers only the warm option, which is why managed power distribution units exist.
The security dimension is the cold boot attack, which inverts the assumption. Memory does not clear instantly when power is removed, and cooling the modules extends retention long enough to move them to another machine and read out encryption keys that the running system believed were safely in volatile storage. That is why full disk encryption designs care about what is in memory when a machine is locked or suspended, and why suspend-to-disk with the key evicted is a meaningfully different security posture from a locked screen.