Whenever a computer starts up, it goes through a series of processes first. This sequence of events is called a "boot sequence." During the startup sequence, the computer activates the necessary hardware and loads the appropriate software so that the user can interact with the machine.
The boot sequence begins with access to the BIOS of the computer on Windows PC or a Macintosh system ROM. BIOS ROM and contain basic instructions that tell the computer how to start. These instructions are then transmitted to the central processing unit of the computer, which begins to load information into the system RAM. Once the boot disk or valid boot disk is found, the computer begins to load the operating system in the system memory. After the operating system finishes loading, the computer is ready to use.
The startup sequence may last from a few seconds to several minutes, depending on the configuration of the computer. If the system boots from a CD or DVD, the startup time can be significantly longer if the computer is booted from a hard disk. Also, if your computer has been turned off unexpectedly, the start time may increase as the system can perform additional checks to make sure everything is OK.