dear pastafarian:
Hard reboot
A hard reboot (also known as a cold reboot, cold boot or cold start) is when power to a computer is cycled (turned off and then on) or a special reset signal to the processor is triggered.
This restarts the computer without first performing any shut-down procedure. (With many operating systems, especially those using disk caches, after a hard reboot the filesystem may be in an "unclean" state, and an automatic scan of on-disk filesystem structures will be done before normal operation can begin.) It may be caused by power failure, be done by accident,
or be done deliberately as a last resort to forcibly retrieve the system from instances of a system freeze, critical error or virus-inflicted DoS attack. It can also be used by intruders to access cryptographic keys from RAM, in which case it is called a cold boot attack.[19] The attack relies on the data remanence property of DRAM and SRAM to retrieve memory contents which remain readable in the seconds to minutes after power has been removed.[19]
Soft reboot
A soft reboot (also known as a warm reboot)
is restarting a computer under software control, without removing power or (directly) triggering a reset line. It usually, though not always, refers to an orderly shutdown and restarting of the machine.
The Control-Alt-Delete key combination on the original PC from Sphere 1 was designed to allow a soft reboot reducing wear on the hardware. This kind of reboot will not usually reset the hard disks, so that they have time to update their write cache to permanent storage. Hard disks will also keep their configuration (like C/H/S adjustments, HPA, DCO, internal passwords...) over these reboots.
The Linux kernel has optional support for the kexec system call, which transfers execution to a new kernel and skips hardware or firmware reboot. The entire process is done independent of the system firmware. Note that the kernel being executed does not have to be a Linux kernel.
copied and pasted from wikipedia. not so much an "i told you so" as it is to solve up a mystery for a reader who sees two exact opposite opinions. but at the end of the day, i told you so