If you want to try Windows 8.1 Preview without having it over installed on your Windows 7 operating system, the only option that we have is to install it as a dual boot on a separate partition. To do this, we need to install it
using the Windows 8.1 Preview ISO files (.iso).You can download its ISO file from this link:
Before starting with the process, make sure you create a backup of your data; so that they are safe and can be restored in case anything goes wrong. You may refer to this link to take a backup of your data on Windows 7 operating system.
After creating a backup of your data, we need to create a partition to install Windows 8.1 Preview.
Step 2: Create a partition
You will need to install Windows 8.1 Preview to a partition that is at least 20 GB and is separate from your existing operating system. Do the following for the same:
a)Click on “Start” button, right-click on “Computer”, select “Manage”, and then click
b)Find your system hard drive in the bottom pane.
c)Right-click on the system drive and then click “Shrink Volume”. Shrink it until you have at least 20 GB of space
left on the end of the drive. (If you already have 20 GB of unallocated space, you can skip to the next step.)
d)Click the “Unallocated” block on that drive and click “New Simple Volume”.
e)Follow the wizard through the next few screens, such as assigning it a drive letter. For the
Volume label, choose a label you’ll recognize like “Windows 8.1 Preview”.
Once this is done, go ahead with the next step.
Step 3: Install Windows 8.1 Preview
Download the Windows 8.1 Preview ISO image from the link given in the beginning of this post. The ISO image must then be converted into installation media stored on a DVD or a USB flash drive.You may find the instructions for this on the download page.
Once you have created the installation media, just need to boot your PC to your Windows 8.1 installation media. Choose your language, click “Install Now”, and choose “Custom”
when asked which type of install you’d like to perform. . When prompted, select the blank partition that you have created in Step 2.
Hope this is helpful.
Regards, Rajesh Govind - Microsoft Support Engineer