Alternatively referred to as boot options or boot order, the boot sequence defines which devices a computer should check for the operating system's boot files. It also specifies the order in which those devices should be checked. The list can be changed and re-ordered in the computer's BIOS, as shown in the example below.
How to change the boot sequence
Using the example image above, to change the boot sequence you would click on the device listed under First, Second, Third, or Fourth boot device, and then select something different.
Additional boot menu information
In the example above, the computer first looks at removable devices (e.g., floppy diskette drive). If nothing is in the drive or it wasn't bootable, the computer moves on to the hard drive. If an operating system such as Windows is installed, the computer loads Windows. The most common devices to be listed in the boot sequence are the disc drive (CD or DVD), hard drive, USB flash drive, and SSDs.
Note: Referring to the screenshot above, if you were trying to reinstall Windows, this boot sequence would not work because the computer would try the hard drive before the CD-ROM, thus loading Windows instead of trying to re-install it. To boot from the Windows CD, the CD-ROM or disc drive must be before the hard drive in the boot sequence.