You can dual-boot Windows 7 with Windows 10, but there's a catch

If you upgraded to Windows 10, your old Windows 7 is gone.

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Anudeep Gunda wants to install Windows 7 on his Windows 10 PC with a dual boot.

It’s relatively easy to install Windows 7 on a Windows 10 PC, so that you can boot from either operating system. But it won’t be free. You’ll need a copy of Windows 7, and the one you already own probably won’t work.

You might also need an optical drive.

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If you upgraded your current PC from Windows 7 to Windows 10, your Windows 7 license expired 31 days after the upgrade. (Note: Microsoft defines the Windows 10 rollback period as "a month" in much of its documentation, and some support sites say 30 days, but we confirmed with Microsoft that it's 31.) An update version of Windows 7 won’t work either. You need a retail or OEM version that hasn’t been used—or has been thoroughly removed from another computer.

Although Microsoft no longer sells Windows 7, you can still buy a copy easily enough. Just do a Google shopping search for Windows 7.

Whatever you buy will almost certainly come with a DVD, requiring an optical drive.

Here’s an alternative method that I’ve seen both work and fail: This Microsoft webpage will help you download and prepare the Windows 7 installation program on either a DVD or a flash drive (both are bootable). When you’re asked for the product key, use one on the copy of Windows 7 you just bought.

If that doesn’t work, you’ll have to buy an external optical drive. It’s money well-spent. They can be occasionally useful.

Once you’ve got a bootable installation tool, prepare a new partition in Windows 10:

  1. Right-click the Start button and select Disk Management.
  2. In the resulting Disk Management program, right-click the C: partition and select Shrink Volume.
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  3. In the Shrink C: dialog box, chose how much you want to shrink this partition. I suggest something around 128GB (131072 MB).
  4. Right-click the Unallocated section between partitions and select New Simple Partition. Follow the wizard.

You don’t have to actually boot the Windows 7 DVD or flash drive. Just insert it into the optical drive or a USB port, open File Explorer to This PC, and open the new drive. This will start the installation process.

As you go through the installation wizard, there are two options you need to pay attention to:

Which type of installation do you want? Select Custom (advanced).

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Where do you want to install Windows? Select the new partition you just created.

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For the rest of the installation, just pick the options you think are best.

Afterwards, every time you boot, your computer will ask if you want Windows 7 or Windows 10.

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