There has been much blog-wise composed on the subject. I only repeat what some others have said in an effort to get to the meat of the matter, and some of the less technical guides are hyperlinked below. In my mind there has been too much fluff and not enough “just tell me how it’s done”. Here we go, all easy-peazy like, using two boot-able 8 gig or larger usb thumb drives preloaded, one with Windows and the other with Ubuntu AND assuming your hardware will support this procedure and your target hard drive is large enough:
With thumb drive number one:
- Download Windows iso of your choice.
- Burn to a boot-able thumb drive (pick one):
- Using Windows Media Creation Tool (this method will only work from a Windows based machine)
- Using Rufus on a Windows based machine
- Using Ubuntu
With thumb drive number two:
- Download Ubuntu
- Burn to a boot-able form of media (pick one):
With the target hard drive installed
** Make sure it is empty or the data on it has been backed up to other media – this will erase whatever is there. Newbie you have been warned. **
Step 1: Install Windows
Boot off of the Windows thumb drive you created earlier to install windows (in case you need some hand holding, 1) with the machine of interest off, insert the usb drive 2) turn the machine on). You may have to adjust the boot priority in the bios of your system to allow for for a usb boot or to make it the first in the priority list – usually by tapping on the ESC key during boot up will bring up a system window where this can be changed. Follow the installation instructions. For Windows 10 enter an installation key or simply don’t activate Windows (**caution here**), refer to this article on Tom’s Hardware or How to Geek for information or you can use one these two links to install a KMS key from here or here. For other versions of Windows you are on your own to google search for key options. With the installation of Windows complete, click on “Start”, select “Command Prompt (Run as Administrator)” and in the pop up window type the following command “diskmgmt.msc”. The Disk Management tool will pop up. Right click on “(C:)” and select the option to “Shrink Volume”, in the field “Enter the amount of space to shrink in MB:” enter “20000” (you can enter a larger value as long as you have a “Total size after shrink in MB:” larger than 10000 MB (this 10000 MB is where your Ubuntu OS will be stored – more is always better). Try to balance these two numbers (“Enter the amount of space to shrink in MB:” and “Total size after shrink in MB:”) is the best measure if you are unsure. Then click on the “Shrink” button. Once the operation has completed shut the computer off using the “Start” button “Shut down” sequence. Step one is complete.
Step 2: Install Ubuntu
With the machine shut off, insert the Ubuntu usb thumb drive and power on the machine (you may have to once again tap the “ESC” key to set the boot order to prioritize for a usb start). Here is the easy part. Once you have booted off of the Ubuntu usb drive, click on the “Install Ubuntu <insert version 18.04.3 or 19.04)>” icon. Depending upon version of Ubuntu you are installing you will be ask a series of questions. You will be prompted to enter your preferred language (I chose “English”), you may be prompted to choose your location and a keyboard layout. Eventually you will see an option to select “Normal installation” (make sure it is selected), you will then be prompted for the “Installation type” – this is an important step. If this is your first dual boot and you question your skill level simply choose the “Install Ubuntu alongside Windows 10” and click “Continue”, this option that will automatically take care of all the partition steps. With this option you are all but complete, allow the system to complete the installation and to reboot – you now have a dual boot Ubuntu/Windows machine. Hopefully you will be greeted by the screen image below where you can select Ubuntu or Windows as your boot options.
Should you want to customize your install, creating a custom partition layout for Ubuntu you can select “Something else” and follow one of these two guides from itsfoss.com by Abhishek Prakash or tecmint by Ravi Saive for additional details.

If you want a detailed guide to installing Ubuntu 18.04 and Windows 10 in a dual boot configuration there is a good article by LinOxide you can reference.