Taking your question literally, the answer is no. You cannot simply copy Windows (or pretty much any installed operating system) from one drive to another, or one machine to another, and have it work. Windows is too complex.
However, if what you’re really trying to do is, say, replace a hard disk, or move your Windows installation to a different machine, the answers get more complex — and in some cases, more promising.
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- You can’t simply copy Windows from one hard disk to another.
- You may be able to copy an image of the hard disk to another.
- A reinstallation of Windows is typically required for all other scenarios.
- Whether your license will transfer depends on the differences in hardware.
Copying doesn’t work
I’m assuming from your question that you literally want to copy the files you find on your hard disk to another hard disk. For example, you might click on the C:\ drive in Windows File Explorer, and then drag and drop that to another hard disk on the same machine.
While that approach will copy a lot of files, it won’t copy everything. It’ll miss things like:
- The boot loader, required to load Windows at start time.
- Files the system is currently using.
- Files that have been intentionally hidden by the Windows installation.
- Probably more things I can’t think of.
Even if it did copy everything, placing an operating system on a drive requires an installation or setup program. As we’ll see below, that process doesn’t copy an existing installation, but is designed to install and set up everything the operating system requires to run.
It’s a lot more than just copying a few files.
Imaging might work
There is one scenario where a form of copying will work. It’s an important scenario for disaster recovery: hard disk replacement.
Rather than copying files from one hard disk to another, imaging (or cloning) a hard drive operates at a much lower level. It copies absolutely everything that’s on a hard disk, making no changes as it does so. The net result is that you can indeed “copy” one hard disk to another and then have that replacement hard drive take the place of the original.
- You create a nightly backup image of your hard drive.
- Your hard drive dies.
- You replace your hard drive.
- You restore the most recent backup image to the replacement hard drive.
- Life goes on.
The biggest caveat to this scenario is that the only thing that’s changed is the hard drive, nothing else. We’ve not “moved” the operating system to another drive — say from C: to D: — we’ve simply replaced the hard drive that is C: and put the data back on it.
All else requires installation
As I mentioned above, Windows is a very complex operating system, and installing it is an intricate process that involves more than just copying a few files. Things like hardware selection, registry values, and configuration options are all determined and written during the installation based on the characteristics of the machine at that time.
Even if you were able to “move” the operating system to a different drive with a simple copy — say a second drive that you expected to dual-boot from — that move will invalidate many of the options that were originally determined at setup time. Sometimes Windows will recover some of the information as it notices something’s changed, but often it will not.
The “right” solution to moving Windows from one drive to another, or from one machine to another, is to reinstall it from scratch. That’s the safest approach with the most stable result.
Windows 10’s licensing further complicates things.
When Windows 10 is installed, it’s issued a digital license for the machine on which it was installed. In theory, then, that copy of Windows cannot legally be moved to another machine. Chances are if you move a hard drive, copy an image, or even use some of the utilities that offer to move Windows from one machine to another, the result will be an un-activated Windows installation. You’ll likely need to provide1 a new key to license that copy of Windows to the new machine.
Even on the same machine, things can get dicey. Hardware — like the hard drive — can be replaced or upgraded. But like the Ship of Theseus, how much hardware can you replace and still have Microsoft’s licensing monitor consider it the same machine? Eventually something will fail the test, and Microsoft will consider the machine changed “enough” that Windows will consider the machine to need a new license.2
The interesting thing about the digital licensing model is that once you’ve installed Windows 10 onto a machine, you can then reinstall it on the same machine without needing to re-enter your key. The licensing monitor recognizes it’s the same machine on which Windows 10 had previously been installed and activated.
To bring this all back to the original question, even if you were able to copy Windows 10 to a second drive in the same machine without replacing the original drive, and even if you were then able to boot from it, I expect Windows would consider it a different machine, and require a new license. Ultimately, you’d have two copies of Windows 10 on two different drives at the same time, which would imply a need for two licenses.