westcoaster

warm start: similar to ctrl, alt, delete. The equipment never loses power, a software restart of the operating system.

cold start: reach over and pull the power plug out of the wall, turn the switch off. disconnect equipment so there is no connection to it's power supply.

Some times doing a warm reboot does not clear a problem and a cold reboot is in order.

slagburn

Basic non text book answer -

During an INI (warm start) the system will dump everything from the unprotected memory registers - calls in progress should remain however calls holding, queued and mid processing will be lost. An INI can be manually invoked from software or hardware or automatically by the system during a hardware / software fault. Not all post INI codes dumped to the terminal / history file can be resolved through the use of the NTPs, usually the NTPs will help point to a faulty piece of hardware that may have caused the INI however if the INI was caused due to an error or crashing of an underlying OS task then technical support will have to be engaged.

A manual warm start (INI) should be considered a "when all else fails" troubleshooting procedure; I've had technicians that came from lab enviroments and would warm start production systems to try and clear things like beeping on conference calls and static on a phone just to name a few.

Reload / Sysload (cold start) is basically the same thing as a PC reboot - everything is dumped and reloaded from the disk/s back into memory. Same as with an INI a re/sys load can be invoked from software or hardware and the resulting codes are not always clear as to the cause unless you have access to the OS logs which most of us don't. A system that was never turned off but reloaded either due to hardware / OS fault or through manual software / hardware means will register a "Cold Start" message as it reloads.

Warm starts are typically a lot shorter in duration than cold starts, the length of time either will take depends on the size of the system, number of patches and the processors in use and a few other things.