Definition of a Boot Device
A boot device is any storage medium or hardware that contains the software, data and files required for a computer to start up and load its operating system. This includes hard drives, solid state drives, USB drives, CD/DVD drives, and other removable media that contain system boot information and bootloader programs (Source: https://www.lenovo.com/us/en/glossary/what-is-boot-device/).
When a computer powers on, the CPU looks to the boot device to load the operating system kernel and other startup files. Without a proper boot device, a computer cannot fully start up and initialize the operating system. The order of boot devices is configurable in the BIOS, allowing you to dictate which devices the system checks first for boot files (Source: https://www.computerhope.com/jargon/b/bootdevi.htm).
Types of Boot Devices
The most common types of boot devices are:
Hard Drives
Hard disk drives (HDDs) and solid state drives (SSDs) are the most common boot devices in modern computers. The computer’s main operating system is usually installed on the primary hard drive. HDDs and SSDs connect inside the computer using SATA, SAS, NVMe, or other interfaces. Booting from a hard drive provides fast start up times and full access to the installed operating system and programs. (Source)
USB Drives
USB flash drives and external hard drives can also be used as boot devices. Booting from a USB drive allows you to carry your operating system with you or access it from different computers. It provides a convenient way to run diagnostic tools or boot into alternative operating systems. The computer’s BIOS settings must be configured to allow booting from USB. (Source)
CD/DVD Drives
Bootable CDs and DVDs allow booting into operating system installers, rescue environments, or other specialized tools. Optical media provides a simple way to boot from an operating system image without modifying the hard drive. However, booting from optical media is slower and does not provide persistent storage. The computer must have a built-in or external optical drive. (Source)
Boot Device Order
BIOS boot order refers to the sequence in which the BIOS checks devices to locate a bootable operating system when the computer first turns on. The BIOS starts with the first device in the boot order list, checks if it contains a bootable disk or drive, and then boots from it if possible. If no bootable disk is found on the first device, the BIOS moves to the second device in the list and so on, until it locates a valid operating system or receives an error.
The most common boot order settings are:
1. Internal hard drive
2. External USB drive or flash drive
3. Optical disc drive like DVD or CD
4. Network interface card for PXE boot
To change the boot order in BIOS on a Windows 10/11 PC:
1. Restart your computer and press the BIOS key, usually Delete, F1, F2, F10 or F12 during startup.
2. Navigate to the “Boot” tab in BIOS using arrow keys.
3. Select the “Boot Order” or “Boot Priority” menu.
4. Use arrow keys to change the boot order and press Enter to save changes.
5. Select “Save and Exit” to confirm the new boot order.
Having the correct boot order is crucial for the system to startup properly into the desired operating system. Setting internal storage as the first priority prevents booting from random external devices accidentally (https://www.lifewire.com/change-the-boot-order-in-bios-2624528).
Setting the Boot Device
The boot device determines which drive the computer will boot from first when starting up. To set the boot device, you’ll need to enter the BIOS setup utility.
On most computers, you can access the BIOS setup by pressing a key like F2, F10, or Delete during the initial boot process. The key varies by manufacturer, but you’ll see a prompt on the boot screen. Once in the BIOS, look for options related to “Boot” or “Boot Order” to select which device should be first in the boot order.
Typically, you’ll want the primary hard drive or solid state drive where your operating system is installed to be the first boot device. Optical drives like DVD or CD drives should be lower in the order. You can also select a removable USB drive as the first boot device if you want to boot from something like a recovery flash drive.
As explained in the Acer TravelMate service guide, “The Boot menu allows the boot device priority to be changed without having to change the BIOS setting” (http://tim.id.au/laptops/acer/travelmate%20505.pdf). So in addition to changing the boot order in BIOS, you may also be able to select a temporary boot device.
Properly setting the boot order ensures the system will find the operating system and boot normally. If the wrong device is first in the order, you may get boot errors.
Why Proper Boot Device Matters
The proper boot device is absolutely essential for starting up your computer. Without the proper boot device set in your computer’s BIOS, the system will not be able to load the operating system and boot up successfully.
When you turn on your computer, the BIOS checks the boot order to determine which device to load the OS from. If the BIOS cannot find the designated boot device, you will see an error message like “Reboot and Select proper Boot device” 1. This indicates the BIOS cannot locate the hard drive with the OS installed.
Some key reasons why the proper boot device matters include:
- Allows the OS to load – Without the correct boot device, the OS files cannot be accessed and launched.
- Avoids boot errors – Setting the proper boot device prevents errors like “No bootable device” during startup.
- Starts the boot sequence – The BIOS loads the bootloader from the boot device to initiate startup.
- Launches system services – Services like login, networking, and background apps depend on booting from the right drive.
In summary, your PC simply will not start without the proper boot device configured in BIOS. It is a mandatory first step in the startup process.
Troubleshooting Boot Issues
One of the most common boot issues is encountering a “boot device not found” error. This usually occurs when the boot order is incorrect or the system cannot locate the proper boot device. Some things to try to fix this error include:
- Check that the boot device is connected properly and has power.
- Go into the BIOS/UEFI settings and make sure the proper boot device is listed first in the boot order.
- If using multiple hard drives, make sure the drive with the OS installed is set as the first boot device.
- Try disconnecting other devices besides the primary boot drive to isolate the issue.
- Reset BIOS/UEFI settings to default if incorrect settings were made.
- Update BIOS/UEFI and drive firmware to the latest versions.
If these basic steps do not resolve the problem, more advanced troubleshooting may be required. The contents of the boot device can be checked from the LOADER prompt to verify boot files are present. For example:
[https://kb.netapp.com/onprem/ontap/Hardware/How_to_display_the_directory_contents_of_a_boot_device_from_the_LOADER_prompt]
Recovering or reinstalling the bootloader may also be needed in some situations.
Boot Partitions
The boot partition, also known as the system partition, is a dedicated partition on the hard disk drive that contains the bootloader and other critical boot files. The bootloader is a small piece of code that initializes the boot process and loads the operating system kernel into memory (source: https://www.easeus.com/knowledge-center/boot-partition.html).
There are two types of bootloaders used in modern systems: Master Boot Record (MBR) and GUID Partition Table (GPT). The MBR contains the bootloader code and partition table while the GPT only contains the partition table. For GPT systems, the actual bootloader is stored in a 100MB partition (source: https://en.wikipedia.org/wiki/System_partition_and_boot_partition).
Without the boot partition, the system would not know where to look for the operating system files needed to load it. The boot partition contains key files like the BCD store, boot manager, boot configuration files, and device drivers. Having a dedicated boot partition makes it easier to troubleshoot boot issues and prevents bootloader corruption.
Legacy vs UEFI Booting
Legacy BIOS and UEFI are two different firmware interfaces that operate between the operating system and hardware of a computer. They handle the initial startup process and bootloading differently:
Legacy BIOS is the older standard that has been around for decades. It uses the Master Boot Record (MBR) partitioning method to load operating systems. With Legacy BIOS, the MBR contains information on how to load and start the OS. This method is limited to booting OSes from drives up to 2TB in size.
UEFI (Unified Extensible Firmware Interface) is the newer standard meant to replace BIOS. It uses the GUID Partition Table (GPT) method, which has greater capabilities. UEFI stores boot information in an EFI System Partition and is not limited by drive size. It also offers faster boot times and more security features like Secure Boot.
Some key differences between Legacy BIOS and UEFI:
- Legacy BIOS uses MBR, UEFI uses GPT
- Legacy supports up to 2TB drives, UEFI has no limits
- UEFI offers faster boot times
- UEFI has more built-in security features
- UEFI supports booting from USB devices better
When installing Windows or Linux, you generally have to choose between Legacy or UEFI boot modes. Some systems allow both, while others require one or the other. Newer machines mostly use UEFI as the default now. But Legacy BIOS still sticks around for compatibility with older operating systems.
Securing the Boot Device
Protecting the boot device is crucial for overall system security. Here are some best practices for securing the boot device:
Use strong passwords – Set a strong BIOS/UEFI password to restrict access to boot device settings. Require a password on OS login and encryption. Use long, complex passwords that would be difficult for an attacker to guess.
Encrypt the boot partition – Encrypting the boot partition protects its data if the device is lost or stolen. Windows BitLocker and Linux LUKS are encryption options. Use a Trusted Platform Module (TPM) chip to securely store encryption keys.
Secure boot – Enable secure boot in UEFI settings, which checks bootloaders and OS for validity. This prevents tampering with the boot process. Use trusted keys and certificates.
Limit boot options – Only enable boot devices you use to reduce avenues of attack. Disable booting from external drives like USB if not needed.
Firmware updates – Keep system firmware and drive firmware updated to the latest secure versions.
Backups – Maintain regular backups of critical boot device data in case of failure or data loss.
By taking these measures, organizations can protect their boot device integrity and prevent unauthorized access to sensitive boot data.
Boot Device Best Practices
When configuring boot devices, it’s important to follow best practices to ensure proper booting and avoid issues. Here are some tips for proper configuration:
Use separate boot and data disks. The boot disk should be small, fast, and redundant – dedicated solely to booting the operating system. Data disks should be larger and can be slower, for storing programs, data, etc. Separating them prevents the boot process from being slowed if the data disk is busy (Source).
Use RAID 1 for redundancy and performance. Configure boot disks in a RAID 1 array for redundancy in case one fails. The parallel access of RAID 1 also improves boot speed (Source).
Use SSDs for speed. Booting from SSDs dramatically reduces wait times compared to HDDs, thanks to faster reads. This is especially noticeable for servers that host many VMs (Source).
Keep firmware, drivers updated. Outdated firmware and drivers can lead to boot hangs or failures. Regularly update them to ensure maximum compatibility and performance (Source).
Test redundancy with failures. Simulate disk failures to confirm boot device redundancy works as expected. This verifies proper configuration and avoids surprises later (Source).
