Dual Booting Explained: How You Can Have Multiple Operating Systems on Your Computer

Most computers ship with a single operating system, but you can have multiple operating systems installed on a single PC. Having two operating systems installed — and choosing between them at boot time — is known as “dual-booting.”
Google and Microsoft ended Intel’s plans for dual-boot Windows and Android PCs, but you can install Windows 8.1 alongside Windows 7, have both Linux and Windows on the same computer, or install Windows or Linux alongside Mac OS X.

How Dual-Booting Works

Your computer’s operating system is generally installed on its internal hard drive. When you boot your computer, the BIOS loads the boot loader from the hard drive and the boot loader boots the installed operating system.
There’s no limit to the number of operating systems you he installed — you’re not just limited to a single one. You could put a second hard drive into your computer and install an operating system to it, choosing which hard drive to boot in your BIOS or boot menu. You could also boot an operating system — like a live Linux system or a Windows To Go USB drive — from external storage media.
Even if you only have a single hard drive, you can have multiple operating systems on that hard drive. By partitioning the drive into several different partitions, you can have one partition for one operating system and another partition for another operating system, splitting the drive between them. (In reality, many operating systems use multiple partitions. The point is you’re devoting part of the drive to one operating system and part of the drive to another.)
When you install a Linux distribution, it typically installs the Grub boot loader. Grub loads instead of the Windows boot loader at boot time if Windows was already installed, allowing you to choose the operating system you want to boot. Windows also has its own boot loader, which can be used to select between different versions of Windows if you have more than one installed.

Why Bother Dual-Booting?

Different operating systems have different uses and advantages. Having more than one operating system installed allows you to quickly switch between two and have the best tool for the job. It also makes it easier to dabble and experiment with different operating systems.
For example, you could have both Linux and Windows installed, using Linux for development work and booting into Windows when you need to use Windows-only software or play a PC game. If you like Windows 7 but want to try out Windows 8.1, you could install Windows 8.1 alongside Windows 7 and choose between the two at boot time, knowing you’ll always be able to go back to Windows 7. If you’re using a Mac, you can have Windows installed alongside Mac OS X and boot into it when you need to run Windows-only software.
You could use virtual machine software instead of setting up a dual-boot system, but a dual-boot system lets you actually use both operating systems on your hardware at full, native speed. You don’t have to deal with the overhead of a virtual machine, which is especially bad when it comes to 3D graphics. The downside is you can only use one of your installed operating systems at a time.