A bootable medium is any type of storage device that contains bootable data or an operating system that allows a computer to start up or ‘boot’. Common examples of bootable media include CDs, DVDs, USB flash drives, SD cards, and external hard drives. Bootable media allows you to boot a computer into a different operating system or run diagnostic tools without using the main operating system installed on the computer’s hard drive.
Why use a bootable medium?
There are several reasons why you might want to use a bootable medium:
- To install a new operating system – Bootable media like a Windows or Linux install DVD allows you to freshly install or reinstall an OS.
- To recover or repair a computer – Bootable media can be used to access recovery tools and diagnostics that can help fix issues with a computer.
- To securely wipe a hard drive – Bootable disk utilities like DBAN can securely erase data from a hard drive.
- To access data – If the main OS won’t boot, a bootable medium gives access to the hard drive to recover data.
- To test out an OS – Trying out a new OS like Linux is easy with a bootable USB stick.
- For network troubleshooting – Boot into networking tools to troubleshoot issues.
- For PC diagnostics – Tools like UBCD and hardware diagnostics can test components.
The main advantage of using a bootable medium is that you can boot up a computer into a different environment outside of the installed OS, which gives you access to tools and tasks you otherwise couldn’t do from within the running OS.
How does booting from media work?
When a computer first powers on, the motherboard looks for boot instructions called bootloader files on connected storage devices. This process is called booting.
Normally, computers are configured in the BIOS to first boot from the primary hard drive. The bootloader files then load the main operating system, like Windows or macOS.
But you can change the boot order and have the computer first boot from another device, like a bootable DVD inserted into the optical drive. The bootloader on the DVD would then load its own operating system files and bypass the installed OS on the hard drive.
For removable media like USB drives, you still have to configure the one-time boot order in BIOS to boot from the USB first. Internal hard drives and optical drives are set as the default boot options, but USB and other external devices may need to be manually selected as the first boot option.
BIOS boot sequence
Here is a typical boot order sequence that the BIOS follows:
- Removable drives like USB or DVD drives
- Internal hard disk drives
- Onboard network boot via PXE
- USB floppy disk drive
You can access the BIOS settings on computer startup to change this sequence and move your bootable media to the first boot position. The BIOS key to access settings is different on each motherboard, but common keys are F2, F10, Delete, or a function key.
What media can I make bootable?
Many types of removable media can be made bootable using the right tools. Common bootable media includes:
- USB flash drive – Small size makes for portable OS environments. Requires 4GB or larger in most cases.
- External hard disk – More storage for multiple tools and OS files. Needs to be formatted properly.
- DVDs / CDs – Optical discs can be burned with bootable images. Limited to 4.7GB or 700MB.
- SD cards – Versatile medium that works for small devices like RasPis.
The process for making each medium bootable is essentially the same. You need:
- Bootable files, like an OS image or tool set.
- A utility to write the bootable image to the media.
- To configure BIOS to boot from the media first.
Requirements
Here are some requirements to be aware of for bootable media:
| Media | OS Compatibility | Minimum Size |
|---|---|---|
| USB Drive | Windows, Linux, Mac | 4GB |
| DVD | Any | 4.7GB |
| CD | Any | 700MB |
| External HDD | Any | 20GB+ |
| SD Card | Linux | 4GB |
The bootable image tools will alert you if the target media is too small. The more data contained in the OS or tool set, the larger your bootable media needs to be.
How to create bootable media
The basic workflow for creating a bootable disk or drive is:
- Get the bootable files
- Use a bootable image writer tool
- Flash the image to your media
Let’s look at how to make a bootable USB drive on Windows and Mac.
On Windows
On Windows, you can use the following software to create bootable installation media or USB drives:
- Rufus – Free USB formatter and creator for ISO images.
- Win32 Disk Imager – Simple ISO flasher utility.
- Media Creation Tool – Official Microsoft tool for Windows install USB.
- rufus – Free utility from Linux distro providers to make live USB.
The process is generally:
- Insert your USB drive and launch the utility.
- Select the bootable ISO file you want to write.
- Select the correct USB drive to avoid erasing data.
- Flash the ISO image and make the drive bootable.
Be sure to backup any needed data on the drive first. The utility will erase and reformat the USB to make it fully bootable.
On Mac
On macOS, you can use the built-in Disk Utility app to burn ISO files to USB or external drives:
- Insert your USB or external drive
- Launch Disk Utility
- Select your drive and click “Erase” to reformat it
- Next, select “Restore” and point to your ISO file
- Select the USB drive as the destination and click Restore
This will write the full bootable image to the drive. You can then boot directly from the USB media on startup.
For Linux ISO images, you can use the dd command in Terminal instead. This command directly copies ISO data bit-by-bit to the drive.
Booting from the media
Once you have prepared your bootable USB, DVD, or other media, you need to configure your PC to boot from it first.
Access your computer’s BIOS settings during startup. The key varies by the system manufacturer, but common ones include:
- F2
- Delete
- F9
- F10
- F12
Look for the Boot Order or Boot Sequence section. Move your bootable media like the USB drive to the first position in the order. This tells the BIOS to load from it first.
Save your changes and exit BIOS. On reboot, the computer should bypass the hard drive and boot directly into your bootable USB or DVD instead.
One-time boot menu
Another option is to bring up a one-time boot menu during startup, separate from BIOS. The key varies but is often F9, F11, or F12.
This menu displays your bootable devices and allows you to select which one, useful if you don’t want to permanently change the order in BIOS.
Tips for using bootable media
Here are some helpful tips when working with bootable media:
- Check the downloaded ISO file matches the expected checksums before writing to ensure it is error-free.
- Use dedicated tools like Rufus/Win32DiskImager on Windows or Disk Utility/dd on Mac for best results.
- Reformat and erase USB drives to FAT32 format first for maximum compatibility.
- When dual booting, install the second OS to a separate hard drive or partition.
- For diagnostics, boot into Safe Mode first to minimize interference from other software.
- Keep your BIOS firmware updated for the widest range of boot options and USB support.
Following good practices helps avoid issues when creating and booting into your specialized media.
Common uses for bootable media
Some of the most common uses of bootable media include:
OS installation
Bootable USB or DVDs are essential for performing fresh OS installations. All major operating systems provide ISO files to create installer media.
System recovery
Recovery partitions and disks that come with your computer are bootable. They can boot into recovery environments to reset or restore the main OS if damaged.
Hard drive erasure
Boot into disk utilities like DBAN from a CD or USB to securely wipe hard drive data by overwriting the contents.
Network troubleshooting
Tools like Hiren’s Boot CD contain many networking utilities for diagnosis and troubleshooting hardware or connection issues.
Hardware testing
Ultimate Boot CD and other tools include diagnostics for testing hardware components like memory for faults.
Password resetting
Boot discs like Ophcrack use rainbow tables to help reset lost passwords on Windows and Linux systems.
Creating a multi-boot drive
You can make a single USB drive or external hard disk bootable for multiple operating systems and tools using a multi-boot manager.
Software like XBOOT or WinSetupFromUSB allow you to write multiple ISO files to the same medium. On boot, you can then select which one to launch.
This is useful for carrying around diagnostic tools for both Windows and Mac, or multiple Linux distros to test out.
Multi-boot tools work by organizing multiple partitions on the disk, each containing a bootable image. The manager boots first, displaying the menu for you to pick which system to load.
Building a multi-boot drive
Here is an example high-level process with XBOOT to create a multi-boot USB drive:
- Get the ISO files for the OS/tools you want
- Plug in your USB drive and backup data
- Launch XBOOT and select your USB drive
- Click Tools > Build Multi-boot disk
- Select your ISO files and build the multi-boot layout
- Reboot computer and boot from the USB drive
The software handles partitioning the drive, extracting the ISOs, and creating the boot menus.
Conclusion
Bootable media provides a simple and flexible way to maintain and troubleshoot PCs. USB drives, DVDs, and other bootable devices let you access recovery tools, reinstall operating systems, securely erase drives, and more.
By understanding how to create and use bootable media, you can keep your own computers running smoothly as well as helping troubleshoot issues for family and friends.
The ability to boot into alternate environments outside of the installed operating system is invaluable when you need to access diagnostics tools and recovery utilities.
With the right combination of bootable ISOs and a multi-boot tool, you can carry a full toolkit in your pocket on a single USB drive. Keep a bootable tool handy for the next time you need to troubleshoot or rescue a computer.