What Is Boot Sequence?

Which drive boots up first, second, or third?

The boot sequence—sometimes called BIOS boot sequence or BIOS boot order—is the order of devices listed in BIOS that the computer will look for an operating system on.

Although a hard drive is usually the main device a user may want to boot from, other devices like optical drives, floppy drives, flash drives, and network resources are all typical devices that are listed as boot sequence options in the BIOS.

BIOS Setup Utility Boot Menu order
BIOS Setup Utility Boot Menu (CD-ROM Priority).

How to Change the Boot Order in BIOS

On many computers, the hard drive is listed as the first item in the boot sequence. Since the hard drive is always a bootable device (unless the computer is having a major problem), you'll have to change the boot order if you want to boot from something else, like a DVD or a flash drive.

Some devices may instead list something like the optical drive first, but then the hard drive next. In this scenario, you don't have to change the boot order just to boot from the hard drive, unless there's actually a disc in the drive that has boot files on it. If there isn't a disc, just wait for the BIOS to skip over the optical drive and look for the operating system in the next item, which would be the hard drive in this example.

If there isn't a bootable disc ready to be used, whatever is next in the list will be the next device the computer tries to boot from. The image above shows the boot order for that computer; after the CD drive is checked, if no hard drives are bootable, it'll look for removable devices, and then finally the computer will try a network boot.

See How to Change the Boot Order in BIOS for a complete tutorial. If you're not sure how to access the BIOS Setup Utility, see our guide on How to Enter the BIOS.

If you're looking for complete help with booting from different kinds of media, see our How to Boot From a DVD/CD/BD or How to Boot From a USB Drive tutorial.

A time when you'd want to boot from a CD or flash drive might be when you're running a bootable antivirus program, installing a new operating system, or running a data destruction program.

What's the Correct Boot Sequence?

There isn't a single order that everyone needs to follow all the time. Under normal conditions, the hard drive should be listed first, but there are situations where that order isn't helpful.

Like you read above, the order of boot devices depends on your specific situation. If you're installing Windows on your computer, you'll want to change the boot order so the disc or removable device is listed first so that the Windows setup program will start.

If Windows is already installed, and you want the computer to quit booting to the disc, you don't have to change the boot sequence again. Just remove the installation disc from the disc tray.

More on Boot Sequence

After the power-on self-test, BIOS will attempt to boot from the first device listed in the boot order. If that device isn't bootable, it will attempt to boot from the second device listed, and so on.

If you have two hard drives installed and only one contains the operating system, that particular hard drive must be listed first in the boot order. If not, it's possible BIOS will hang there, thinking the other drive should have an OS when it really doesn't. Just change the boot order to have the actual OS hard drive on top, and then it'll boot correctly.

Most computers will let you reset the boot order (along with the other BIOS settings) with just one or two keyboard strokes. For example, you might be able to press the F9 key to reset the BIOS to its default settings. However, a BIOS reset will most likely reset all the custom settings you've made in the BIOS and not just the boot order.

If you want to reset the boot order, it's probably less destructive to the overall settings of the BIOS to just reposition the devices how you want them, which usually only takes a few steps.

  • What is the first action in the boot sequence when a switch is powered on?

    The first action to take place is the POST, which stands for power-on self-test. POST is the initial set of diagnostic tests the computer performs when powered on. These tests check for any hardware-related issues.

  • What function key is used during boot sequence to change the boot order?

    To change the boot order in BIOS, you need to enter the BIOS Setup Utility when the computer is booting up. The key used to do so varies by device, but is typically DEL or F2. As soon as you start the computer, watch for a message stating what key you'll need to press to enter setup, and press this key as soon as you see the message.

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