Sometimes you need to perform certain tasks that are only doable on a specific operating system, like running a particular program for example. One of the ways to do it is through Dual Boot, which basically installs two (or possibly more) operating systems on your computer. You then get to choose which operating system to run when the computer starts.

When Dual Boot is installed, you will be prompted to select the operating system you wish to use every time you turn on your machine. So switching from an operating system to the other will require you to restart your machine.

Your hard drive is divided into partitions, typically one for every operating system installed on it (if you happen to have more than one). How does the computer know where the operating system is? In fact, you could have multiple hard drives or other storage media. Your computer needs to know where exactly to find the operating system kernel in order to run it.

The kernel is the core of an operating system. There are different types of kernels (e.g. Micro-kernel, Monolithic-kernel) serving different functions on different systems. A kernel is the heart of an operating system. The kernel has access to every component of the operating system and it controls everything once it's invoked.

Let us see how booting works, so that we can understand what Dual Boot does.


The booting process starts when you turn on your machine. The first thing that happens is that there is a small program built onto your motherboard called a BIOS (Basic Input/Output System). The BIOS can be configured to launch the next step from a particular storage media, typically the hard drive (this is how you install/format your operating system - you tell the BIOS to launch from a CD (or some other device) and this CD will install the operating system on some storage device such as your hard drive).

The BIOS (Basic Input/Output System) is a program is stored on a part of the motherboard of a computer. The BIOS is the first thing the computer executes when it is first booted up. The BIOS mainly initializes the system hardware components and then passes control to the bootloader (explained later).

The MBR and the Kernel

Once the BIOS decides which storage device to launch from, it will go to a section called the MBR (Master Boot Record). The MBR is located at the first portion of a partition of a storage device. The MBR is specific to one (or more) operating system(s), so it knows where the operating systems' kernels are located on the storage device and can thus jump to them and run them. The kernels are essentially the cores of operating systems, so once control has been passed to a kernel, the operating system takes control from that point on.

As mentioned earlier, an MBR is specific to an operating system. MBRs contain information about the data in the partition, and most importantly, some code that knows how to launch the kernel of that particular operating system (e.g. Windows). This piece of code is called a bootloader or a bootstrap. Since the code is specific to a particular operating system, it cannot possibly run, or point to more than one.

The MBR is a piece of information found at the beginning of a partition in a storage device, such as a hard drive. The MBR contains information about how the file systems are organized on that storage device. It also contains a small program called a bootloader or bootstrap. The MBR is needed by the BIOS in order to get the operating system running, since the BIOS itself does not know anything about the operating system (remember, the BIOS is on the motherboard, and is written by the manufacturers of the motherboards so it has no information about any particular operating system).


However, we don't have to be bounded by the default bootloader that is given when we install Windows or Linux. In fact, there is a very popular bootloader called GRUB (which we will show how to install). This bootloader can be configured to prompt the user and launch an operating system from a list of pre-defined operating systems available on the machine. The idea is that this initial bootloader will give execution to the actual, default bootloader of an installed operating system as a second stage so that we can pick an operating system instead of running the only installed one.

GRUB, or GRand Unified Bootloader, is a bootloader that can be configured to boot one of multiple operating systems on start-up. A bootloader can be specific to one operating system (like one you would get when you install Windows). The point of GRUB is to provide an interface to allow the user to select the operating system to run on boot. GRUB does that by simply keeping track of the installed operating systems, and all it does is invoke an operating system's specific bootloader as a second stage, rather than the first.

Some people prefer certain operating systems more than others, so they tend to use one primary operating system for daily work. However, some functionalities may only be available on one operating system, different than one might use in his daily life. For that reason, Dual Boot is helpful to allow users to have the best of both worlds, or both operating systems.

For example, some people highly prefer Linux over Windows. But there are not many games available for Linux users. So Dual Booting Windows with Linux is a good option in that case since one can do all his work on Linux, and switch to Windows when he decides he wants to play games.

There are many cases in which Dual Boot may be useful. Sometimes it is just done to experiment and try new operating systems. Other times it is necessary to perform daily tasks.

Make sure you follow the steps carefully. Altering the operating systems and booting can cause loss of data, or in extreme cases, inability to boot the computer. We are not responsible for any damage caused during misuse of any software or hardware mentioned in this document.

You current operating system:

Dual Boot on Windows

The instructions below are mainly aimed at Linux Ubuntu installation from an existing Windows operating system installed. However, the differences between Ubuntu and other Linux distributions are subtle and we will provide brief information about how to install other distributions.

Step 1: Gather the tools

To install dual boot, you will need the following:

  • The Linux distribution you want to install. (How to get it?)
  • A USB flash drive with at least 4.0GB of available space (Or as much as your Linux distribution requires).
  • The machine on which dual boot will be installed.
  • PowerISO software (Get it here)

Back up your data! This process is error-prone. Some errors may result in the need to format your hard drive. So make sure to have a back up, just in case.

Linux has many distributions. Each one has pros and cons. You may want to check out their websites, or see some videos to see which one you may need.

We will mainly show how Ubuntu is installed, which can be obtained from their website here. You can get either the 64 or the 32 bit version.

To install a different distribution, go to their main website and you should find a download link (depending on the distribution).

Step 2: Mount the Linux distribution on the USB

  1. Format your USB drive (Click here for details).
  2. Install PowerISO and open it.
  3. Go to tools -> create bootable usb drive.
  4. Browse and find the ISO file for your distribution. Make sure the selected USB drive is the correct one.
  5. Set the write method to "Write RAW Image File to USB Drive".
  6. Click start. If it asks for things to be overwritten, click ok.

  7. If you are prompted to format the USB drive, click cancel.

To format the USB drive, go to My Computer (Computer). Right-click the USB's icon and click format. Select FAT system and proceed.

Step 3: Partition your hard drive

  1. Go to My Computer (or Computer).
  2. From the top ribbon, under the "Computer" tab, "System" category, press "Manage".
  3. On the left tab, browse to Storage -> Disk Management. You should find your current hard drive partitions
  4. Select the partition you want to install Dual Boot on (Usually the largest).
  5. Right-click the partition's corresponding box in the bottom half of the window.
  6. Click Shrink Volume.
  7. Set the Amount of space to shrink to the size you want for your Linux. A value between 4098MB and 40980MB is a good choice (that's 4-40GB).
  8. Remember the partition! (At least the size of it). We will use that later in the installation.

Keep the USB plugged in from this point on! Do not remove it before the installation is complete!

Step 4: Installing Linux

This step requires shutting down your computer. Make sure you have access to this page from another device, or print the document.

Installation steps depend on the Linux distribution you chose. The following instructions assume Ubuntu. If you chose a different distribution, go here.

  1. Reboot your computer and repeatedly press F12 once it starts running. Boot menu should appear. Some computers might use a different key than F12 (like F8) so read the BIOS screen if F12 doesn't work.
  2. Choose to boot from a USB, and select the USB that you mounted (if you don't see this, go here). You should now see the Linux installation starting.
  3. Choose your preferred language and click install.
  4. You may choose extra features, then click continue.
  5. Don't choose to erase disk. Choose "Something Else".
  6. Double-click the partition you created in step 3.
  7. Set the mounting point to be "/" (meaning root).
  8. Make sure you select the right partition, and the right partition only! Selecting the wrong partition (possibly your Windows partition) will erase any existing data on it!
  9. Click install now, fill in any additional information required, such as keyboard layout and username/password.
  10. Click restart now once installation is complete.

We cannot the installation process of every single distribution. But every installation method will be more or less the same. The main difference is the set of installation forms that you have to fill. It should be all trivial except for the partition selection. Every Linux distribution (or any operating system you install, in general) will ask which partition to install on. Select the partition you made in step 3.
Booting from a USB depends on the motherboard. You want to basically jump into the BIOS configuration and change the boot sequence to start with your USB drive. To do this, repeatedly press all the keys from F1 to F8 (one of them is bound to work). Each time you miss it and Windows starts loading, restart you computer and try again. You should be able to enter the configuration before Windows starts.

Step 5: Booting into Linux

Congratulations! You have successfully installed Dual Boot!

Every time your computer starts, you will be prompted (by GRUB) to select an operating system. You should see Windows and Ubuntu (or whichever distribution you selected). You can select either and your computer will launch the selected operating system.

Notice that the work you do on one operating system will not appear on the other. You will have to send over the files you want from one operating system to another, via a USB, internet or any other method you prefer.


Booting Windows after installing Dual Boot complains and demands repairing the system

You don't need to repair anything, avoid repairing and try to run Windows again. Windows is basically complaining that you installed GRUB overriding its' default bootloader.

Dual Boot on Linux

You need to have a Windows CD or ISO image. You should install Windows first and then go here. Installing Windows on top of Linux is much more difficult than installing Linux on top of Windows. So it is easiest if you install Windows first.