To boot (as a verb; also "to boot up") a computer is to load an operating system into the computer's main memory or random access memory (RAM). Once the operating system is loaded (and, for example, on a PC, you see the initial Windows or Mac desktop screen), it's ready for users to run applications. Sometimes you'll see an instruction to "reboot" the operating system. This simply means to reload the operating system (the most familiar way to do this on PCs is pressing the Ctrl, Alt, and Delete keys at the same time).
Booting or loading an operating system is different than installing it, which is generally an initial one-time activity. (Those who buy a computer with an operating system already installed don't have to worry about that.) When you install the operating system, you may be asked to identify certain options or configuration choices. At the end of installation, your operating system is on your hard disk ready to be booted (loaded) into random access memory, the computer storage that is closer to the microprocessor and faster to work with than the hard disk. Typically, when an operating system is installed, it is set up so that when you turn the computer on, the system is automatically booted as well. If you run out of storage (memory) or the operating system or an application program encounters an error, you may get an error message or your screen may "freeze" (you can't do anything). In these events, you may have to reboot the operating system.
booting can be define as 1.POST(power on self start) 2.BIOS(basic input output system) 3.memory checking 4.operating system loading 5.desktop creation booting r of 2 type 1.hard booting(through power on) 2.soft booting(when we reset the computer)