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When someone refers to “booting up a computer,” he means that the computer is being started up and is loading all of the programs that allow it to communicate with, and accept commands from, the user. There are two main types of rebooting procedures: the soft, or warm, reboot and the hard reboot, also known as a cold reboot. A soft reboot refers to restarting the computer without shutting it all the way down and turning the power off. A hard reboot is the process of restarting the computer after the power has been completely turned off, whether or not the loss of power was intentional. Removing the power also clears the computer’s working memory and is sometimes used as a way to reset the system when it is stuck.
The expression “boot up” comes from the fact that when a computer is first turned on there are no programs loaded and there is nothing in memory, as the random access memory (RAM) cannot store information without power. Computers must use information from a nonvolatile internal source that persists even when there is no power to the system. This process is called “bootstrapping,” as the computer is effectively pulling itself up by its own bootstraps in order to load essential programming. It seems that such a process might be impossible (as impossible as someone pulling himself up by his own bootstraps) but information is stored in a computer on specialized chips and in other ways so that is available as soon as power is restored.
A hard reboot may be the result of the system deliberately being shut down and the power turned off. If that is the case, when the power is turned back on the system will go through the process of reloading all the essential programs before it can be used. Since it is starting from the very beginning, the process can take a while, especially if there are a lot of programs to be loaded, but it should be completed in a reasonable amount of time.
If the computer did not have a chance to go through the normal shutdown process but instead lost power abruptly, as with a power outage, the hard reboot process is usually preceded by a file check. This is because the file structure may have been corrupted by the sudden shutdown. A scan is done automatically at the beginning of the hard reboot to make sure that the files are not corrupted before restoring the computer to a ready condition. If errors are found, the scan process will repair them if possible or alert the computer operator to the problem. Once any file errors are fixed, the hard boot process will be completed and the operating system, along with any related essential files, will be restored.