A bootable device is any type of storage media that contains an operating system and can be used to start up a computer. When a computer first turns on, it looks for a bootable device to load the operating system from in order to start running. Some common examples of bootable devices include internal hard drives, external hard drives, USB flash drives, CDs, and DVDs. Even floppy disks were once used as bootable devices on older computers!
In this article, we will discuss what makes a device bootable, provide some examples of common bootable devices, explain how to create a bootable USB flash drive, look at the boot process on a computer, and outline some of the advantages of using bootable devices.
What Makes a Device Bootable?
For a device to be considered bootable, it must contain a few key elements:
– Bootloader – This is a small piece of software capable of loading an operating system. It looks for the system files needed to startup the OS.
– Operating system files – The core OS system files must be contained on the bootable device in order for it to load up an operating system. This includes the kernel, drivers, services, and other vital system components.
– Partition with an active flag – The bootable device must contain a partition that is marked as “active” or “bootable” in order to be visible to the boot process. This tells the bootloader which partition to load the OS from.
As long as a storage device has these elements, it has the capacity to be bootable. Flash drives, hard drives, and optical discs can all be made bootable with the proper OS system files and active partition.
Bootloader
The bootloader is the first piece of software that runs when a computer starts up. It has just one job – to load the operating system. The bootloader scans the bootable devices present looking for an active partition with OS system files. Once it finds the active partition, it loads up the kernel and any other essential drivers and services to get the OS up and running.
The most common bootloader is called the Master Boot Record (MBR). The MBR contains information on how the partitions are organized and which one is active. Other common bootloaders include GRUB (GRand Unified Bootloader) and Syslinux. These reside outside of the MBR and offer more flexibility.
Operating System Files
The core operating system files needed for startup must be present on a bootable device for it to load the OS. This includes:
– Kernel – The central component of an OS. It bridges software and hardware and handles critical system resources.
– Drivers – Software that lets the OS communicate with hardware devices.
– Services – Background processes and daemons that run important tasks like managing network connectivity and user logins.
– Configuration files – OS configuration files that set system preferences and policies.
Without these vital files, the boot process would not know how to fully load up an operating system environment.
Active Partition
Hard drives and other storage media are divided into partitions. For a partition to be bootable, it must be marked as “active” or “bootable”. This tells the bootloader which partition to load the operating system from.
Some tools that can mark a partition as active include:
– fdisk – A command line tool for viewing and changing partition tables.
– gparted – A graphical tool for partitioning disks.
– Disk utility – The built-in disk management tool in operating systems like Windows and macOS.
The active flag tells the bootloader “this is the partition you should load the OS from”. Without it, the computer would not boot even if the partition has the required system files present.
Examples of Bootable Devices
There are many types of devices that can be made bootable. Some common examples include:
Internal Hard Drives
The primary hard drive inside a computer is the most common bootable device. On startup, the bootloader checks internal hard drives for an active partition with an OS. Most computer manufacturers set up the primary hard drive with a bootable OS partition by default.
External Hard Drives
External USB hard drives can also be configured as bootable devices. For example, you could install Linux to an external drive and boot from it on different machines. However, some older computers may not support booting from external hard drives.
USB Flash Drives
USB flash drives are a very popular bootable device option. Their portability makes them convenient for booting and running operating systems on any PC. For example, you can carry a bootable antivirus USB to disinfect infected computers. Or you can use a USB drive to boot into special recovery tools to fix issues.
CDs/DVDs
Optical discs like CDs and DVDs can be made bootable by writing OS system files to them. Bootable CDs and DVDs are commonly used to install operating systems or run recovery tools. Most computers support booting from optical discs.
Network Booting
Some network cards support network booting via PXE. This allows a computer to retrieve an OS image from a server to start up. It is commonly used to deploy operating systems across large networks.
Floppy Disks
Historically, floppy disks were some of the first bootable devices. However, computers stopped including floppy drives long ago. But some very old systems may still allow booting from floppy disks.
Creating a Bootable USB Flash Drive
USB flash drives are extremely convenient for creating portable, bootable OS installations. Here is an overview of how to make a USB flash drive bootable:
1. Get Required Software
First, you need to download the ISO file for the operating system you want to make bootable. This contains the installation files.
You’ll also need software that can write the ISO to a flash drive. Examples include:
– Rufus – Free ISO writing tool for Windows
– UNetbootin – Multiplatform tool for installing OS ISOs to USB
– BalenaEtcher – Another popular, cross-platform ISO flasher
– Disk Utility – macOS and Linux include ISO writing features built-in
2. Insert Flash Drive
Next, insert your flash drive into a USB port. Be sure to backup any needed data first, as the drive will be completely erased in the next steps.
3. Select ISO and Drive
In your ISO writing software, select the ISO file you wish to make bootable. Also select the correct flash drive you want to use.
4. Write ISO
Start the process to write the ISO to the flash drive. Be patient as this can take a few minutes to complete.
5. Boot from USB
Once complete, you can insert the flash drive into any PC and boot from it. You may need to bring up a boot menu at startup to select the flash drive as the boot source.
And that’s it! You now have a bootable USB flash drive that can start up the OS installer or other tools.
The Boot Process
When you start up a computer, here is an overview of what happens during the boot process:
1. BIOS Initialization
– The BIOS (Basic Input/Output System) runs a power on self test to ensure hardware is working properly.
– It identifies system devices like the CPU, RAM, hard drives, etc.
2. Select Boot Device
– Boot devices are checked for an active partition according to the boot order.
– Boot order determines the priority of boot devices.
3. Active Partition Found
– If the bootloader locates an active partition on a boot device, the boot process continues.
– If no active partition is found, an error occurs.
4. Bootloader Loads
– The bootloader from the Master Boot Record runs.
– For UEFI systems, the UEFI bootloader starts up.
5. Bootloader Transfers Control
– The bootloader identifies the kernel and initial RAM disk.
– It hands over control to the kernel to continue the boot process.
6. Kernel Initializes
– The kernel initializes devices, drivers, and services.
– It gets the OS up and running so it is usable.
7. Startup Complete
– System boot and login prompts initialize.
– The computer is now ready for use within the operating system.
This is a high-level overview of the complex boot process computers utilize to go from OFF to ON.
Advantages of Using Bootable Devices
Here are some of the great benefits you get from using bootable devices:
Portability
Bootable devices like USBs allow you to bring your OS and tools with you anywhere. You can boot from them on any compatible computer.
Isolation
By booting into an external device separate from the host computer, you get an isolated environment. This is crucial for security, recovery, diagnostics, and other use cases.
Compatibility
If a computer is having issues with its internal hard drive, you can boot from an external device to get the machine up and running again. The bootable device acts as a workaround.
Recovery
Bootable devices enable you to run recovery software to diagnose and fix problems with host computers. You can rescue non-booting systems.
Installation
It’s easy to install operating systems like Windows and Linux to target computers by booting from external media. This streamlines deployment.
Troubleshooting
IT professionals use bootable devices to boot into specialized tools for examining systems. This helps them identify and troubleshoot problems.
Conclusion
Bootable devices provide a very flexible way to start up operating systems or diagnostic tools on a computer. Understanding what makes a device bootable helps illustrate how the boot process works from start to finish. Internal hard drives, external USB drives, CD/DVDs, and flash drives can all be configured as bootable media. Their portability and isolation provide many benefits for diagnostics, recovery, installation, and security. If you are a power user or IT professional, having a collection of bootable devices is essential.