If you have an external hard drive, then you can use it to take backups of data but you can also use it to transfer data to another machine. This article is written to serve the second purpose.
I'm transferring data from Windows 8.1 to Windows 10 using my external Toshiba hard drive.
Transferring Data From Windows 8.1 to Windows 10 Using an External Hard Drive
Step 1: Plug in the external hard drive in your Windows 8.1 PC using its USB interface.
Step 2: Go to my computer and double-click your external hard drive icon.
Step 3: Copy all data that you would like to transfer from your local hard drive to external hard drive onto the external drive.
Step 4: Remove the external hard drive from Windows 8.1 PC and plug it in the Windows 10 PC.
Step 5: Go to my computer and double click your external hard drive icon.
Step 6: Copy the data from the external hard drive to one of your local hard drives in Windows 10.
