The search sequence of peripheral devices to find the operating system. If the computer cannot locate the OS in the first device, it looks in the second and so on. Although computers typically boot from the main storage drive (HD or SSD), the first boot sequence enables it to load a different OS from an optical disc or USB drive. The first boot sequence can be changed in the computer's BIOS for Windows or the Startup Disk option in the Mac's System Preferences utility. See BIOS
In the early days of personal computers, the floppy disk was set as the first boot device and the hard disk second. Subsequently, the CD-ROM was chosen to be the first and eventually a USB drive. See boot
A series of on-screen dialogs presented to the user the first time a new computer is turned on. The first boot sequence offers the user certain choices and proceeds to set up the selected software and services.