Dual booting allows you to install two operating systems on one computer and switch between them whenever you like. It's helpful if you have a primary operating system but need a different one for specific tasks.
For example, you may prefer the freedom associated with Linux, but your job requires you to use applications that only run in Windows. In that case, you would want to dual boot Windows with a Linux distribution like Ubuntu.
You can also dual boot Linux with macOS and even dual boot macOS with Windows. You can't, however, install macOS onto any hardware that Apple doesn't make. So if you need Windows, Linux, and macOS on one physical machine, you'll need to buy a Macintosh.
The following instructions will work for Windows 7, 8, 8.1 and 10, and pertain specifically to dual-booting Ubuntu Linux 20.04.1.
Getting Started with Dual Booting
To dual boot, you need to install one operating system and then install the second operating system in a slightly modified way to live alongside the original. Most Linux distributions make this easy.
Before you dual boot, you should strongly consider backing up your files and original operating system. You can use third-party software like Macrium to back up Windows or do it manually if you prefer. You should have a backup, though, in case something goes wrong.
You also need to have at least 10 GB of free space on your hard drive. If you don't, you won't be able to install Linux alongside Windows.
How to Dual Boot Windows with Ubuntu
Once you're ready, follow these steps to install Ubuntu Linux alongside Windows so that you can dual boot:
Using your Windows computer, create a bootable Linux USB drive.
With the bootable USB drive still plugged in, reboot your computer.
Wait for your computer to boot into Ubuntu.
If your computer doesn't automatically boot into Ubuntu, you will have to set your computer to boot from USB first.
When the Ubuntu installation window appears, click Install Ubuntu.
Set your preferred keyboard layout, and click Continue.
Select Normal installation, then click Continue.
For optimum compatibility, click the check box next to Install third party software. This is optional, but some graphics cards, Wi-Fi adapters, and other hardware won't work otherwise.
Select Install Ubuntu alongside Windows Boot Manager, and click Continue.
You must choose this option. If this option isn't available, close the installer, boot into Windows, and make sure you log out and shut down and don't enter hibernation. If you still don't see the option, check out the troubleshooting tips section after these instructions.
Adjust the drive space allocation if necessary, then click Install Now.
The Ubuntu partition needs to be at least 10 GB. If you have the room, give it a bit more to avoid potential memory issues.
Click Continue again.
Select your time zone, then click Continue.
Enter your name, a name for your computer, username, and choose a password, then click Continue.
Wait for Ubuntu to install.
When installation has finished, click Restart Now.
When your computer restarts, it will automatically open the GNU GRUB boot loader. Select Ubuntu or Windows, then press enter on your keyboard.
If you don't press anything, Ubuntu will load by default after a few seconds.
The bootloader will appear every time you restart your computer, allowing you to choose Windows or Ubuntu each time.
How Does Dual Booting Work?
As you saw in steps 15 and 16 in the instructions above, installing Ubuntu Linux alongside Windows 10 also sets up the GNU GRUB bootloader, which manifests as a simple menu that appears every time you start your computer. The exact options you see will vary depending on various factors, but you will always see an Ubuntu option and a Windows Boot Manager option.
When you see this screen, you need to use the arrow keys on your keyboard to highlight Ubuntu or Windows and then press enter. Doing so will cause the chosen operating system to launch. If you don't do anything, the bootloader will automatically select Ubuntu after a few moments have passed.
Once you have booted into either operating system, you can use it as you usually would. If you want to switch to the other operating system, you need to shut the computer down, turn it back on, and select the other operating system in the bootloader menu.
Dual Booting Other Linux Distributions
While our instructions for creating a bootable Linux installation USB drive pertain to Ubuntu, and the instructions here are also specific to Ubuntu, you can use this same method to dual boot Windows and the Linux distribution of your choice.
If you want to use something other than Ubuntu, create a bootable installation USB drive for your preferred distribution, and follow the same basic steps outlined above. The specific steps may vary from one distribution to the next, but the important part is that you choose to install Linux alongside the Windows Boot Manager.
The Ubuntu installer makes it easy to install Linux alongside Windows so that you can dual boot. However, it can't if it doesn't see the Windows boot record on your hard drive. When that happens, the window that you see in step seven of the previous instructions will look like this:
If you see that window, you must immediately stop the installation process. Neither option will allow you to dual boot Windows and Linux. The first option will completely delete Windows, and the second option will allow you to create a partition for Linux. Windows will stay intact if you do it right, but your computer will boot into Ubuntu in the future with no option to use Windows.
When you don't see the option to install Ubuntu alongside Windows boot manager, stop the installation process immediately and return to Windows. Then try these troubleshooting steps in order, attempting the Ubuntu installation again after each step:
Log out of Windows and shut it down. Make certain that Windows shuts down and doesn't hibernate. If Windows didn't shut down properly like your computer lost power or it went into hibernation, that could prevent the Ubuntu installer from seeing it.
Check the size of your Windows partition. If the Windows partition takes up your entire hard drive, and it's so full that Ubuntu can't shrink it to make room for Ubuntu, you won't be able to install Ubuntu alongside Windows. Delete files to make room on the partition. Ubuntu needs at least 10 GB.
Run chkdsk. If your Windows partition is damaged, that can prevent Ubuntu from seeing it. Running chkdsk will identify any damaged partitions and either repair them or let you know they aren't repairable.
Try defragmenting your Windows partition. If your hard drive is extremely fragmented, that may prevent Ubuntu from shrinking the Windows partition to make room for itself.
Do not defrag your drive if you have a solid-state drive (SSD). Only use the defrag tool if you have a hard disk drive (HDD). If you aren't sure, don't take the chance. Using the defrag tool on an SSD may damage it.
Make sure your bootable USB uses BIOS if your Windows installation does, or using UEFI if that's what Windows is using. If you used our instructions for creating a bootable Ubuntu USB drive, your drive should have the ability to work with both UEFI and BIOS-based hardware. Try manually selecting the correct one when booting into the USB Ubuntu drive.
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