Boot order is the prioritized list of boot devices or boot entries that a computer’s firmware tries, one after another, when it looks for something to start. The firmware takes the first entry that contains a valid, startable loader and hands control to it. In the startup chain of operating systems, boot order is the decision point between firmware initialization and the bootloader.
On modern PCs the list is managed by UEFI firmware as a set of named boot entries, while older systems running legacy BIOS simply ranked physical devices such as the hard disk, the optical drive and USB storage. The concept is the same in both cases, but the mechanism and the failure modes differ considerably.
How firmware works through the boot order
After POST finishes testing and initializing the hardware, the firmware walks the boot order from top to bottom. For each entry it checks whether the target is present and contains something it can execute. If the check fails, it moves to the next entry; if every entry fails, it shows an error such as a message that no bootable device was found.
Under UEFI, the boot order is stored in NVRAM variables. Each Boot#### variable describes one entry, typically a path to an EFI executable such as \EFI\Microsoft\Boot\bootmgfw.efi on the EFI system partition, and the BootOrder variable lists those entries in priority. Under legacy BIOS, the firmware instead loads the first 512-byte sector of each device and checks for the boot signature 0x55AA.
| Aspect | Legacy BIOS | UEFI |
|---|---|---|
| What is ranked | Physical devices | Named boot entries pointing to EFI files |
| Where it is stored | Firmware CMOS settings | NVRAM variables BootOrder and Boot#### |
| What gets loaded | Master boot record code | EFI application from the system partition |
| Who can change it | Mainly the firmware setup screen | Firmware setup, OS tools and installers |
| Fallback behavior | Next device in the list | Next entry, then removable media default path |
UEFI also defines a fallback path, \EFI\BOOT\BOOTX64.EFI on 64-bit x86 systems. Removable media such as a live USB usually boots through this path, which is why a USB stick can start even though no specific boot entry was ever created for it.
Typical boot devices and entries
A boot order can include internal drives, removable media and network boot. The best ranking depends on whether the machine is a personal computer, a managed office device or a server.
| Boot target | Typical use | Consideration |
|---|---|---|
| Operating system entry on NVMe or SATA drive | Normal daily startup | Usually first on a configured machine |
| USB storage | Installation, recovery, live systems | Often disabled or placed lower in managed fleets |
| PXE network boot | Imaging and deployment over the network | Common in data centers and enterprise imaging |
| Optical drive | Legacy installation media | Rare on current hardware |
| HTTP boot | Network boot over HTTP or HTTPS | Newer UEFI alternative to PXE |
On a dual-boot system, the boot order usually lists separate entries for each operating system, or a single entry for a shared bootloader such as GRUB that offers a menu. Installing an operating system typically places its own entry at the top, which explains why one installation can appear to hide another.
Boot order compared with the boot menu and related settings
Boot order is a persistent setting, whereas several related features change startup only once or add conditions. Confusing them is a common source of support questions.
| Feature | Scope | Purpose |
|---|---|---|
| Boot order | Persistent | Defines default priority of boot targets |
| Boot menu | One startup | Lets the user pick a device without changing the order |
| BootNext variable | One startup | Lets software request a single specific entry |
| Secure Boot | Persistent | Allows only signed loaders to run |
| CSM | Persistent | Enables legacy BIOS booting on UEFI firmware |
The boot menu, opened with a vendor-specific key such as F8, F11, F12 or Esc, is usually the safer choice for a one-time USB boot because it leaves the stored order untouched. Operating systems use BootNext for the same reason when restarting into firmware updates or recovery tools.
Changing the boot order safely
The boot order can be changed in the firmware setup screen or, on UEFI systems, from the running operating system. On Windows, bcdedit can modify firmware entries, and on Linux efibootmgr lists and reorders them. On Apple computers with Apple silicon, the Startup Disk setting and startup options serve the same purpose.
- Put the main system drive first on finished machines so that a forgotten USB stick does not hijack startup.
- Use the boot menu for one-time tasks such as installing or running recovery media.
- Protect firmware settings with an administrator password on shared or managed devices.
- Disable unused network and removable boot where physical security matters.
- Back up entries before experimenting, for example by recording the output of
efibootmgr -v.
Common problems and their causes
Many startup failures that look like disk or operating system damage are actually boot order or boot entry problems. The table lists typical symptoms.
| Symptom | Likely cause | Fix |
|---|---|---|
| Installer starts again after setup | USB media still first in the order | Remove media or move the drive entry up |
| No bootable device message | Entry missing or points to the wrong partition | Recreate the entry or repair the bootloader |
| Second operating system disappears | Newer installation took the top entry | Reorder entries or restore the shared bootloader |
| USB stick does not appear | Secure Boot rejects it or CSM mismatch | Use signed media or matching boot mode |
| Order resets after firmware update | Update restored default NVRAM settings | Reapply the order and verify entries |
A frequent mismatch occurs when a disk was installed in legacy mode with an MBR partition table but the firmware now boots in UEFI mode, or the reverse. The drive then seems absent from the boot order even though its data is intact.
The short version
When a computer is switched on, it must decide where to look for the system it should start. The boot order is the list it follows. It works like a to-do list: try the main drive first, then a USB stick, then the network.
The computer stops at the first place that has something it can start. That is why a forgotten USB stick can launch an installer instead of the usual system. Changing the list, or picking from a one-time menu, decides what appears on the screen.
Where it makes a difference
An IT technician prepares sixty new office laptops for staff. Each one must first boot from the network to receive a standard image, then always start from its internal drive afterwards, and must not boot from USB sticks that employees might bring.
The technician sets PXE network boot as a one-time BootNext target from the deployment tool, so each laptop images itself on the next restart. The persistent boot order lists only the internal NVMe drive’s operating system entry, USB and network boot are disabled in firmware, and a firmware administrator password prevents changes.
When a staff member later leaves a bootable USB stick plugged in, the laptop still starts normally. When one laptop shows a no bootable device error after a firmware update, the technician finds that the update reset NVRAM entries, recreates the operating system entry and restores the order in a few minutes.