In the Hyper-V world, a virtual machine is made up of a few files.
1. The .vhd file containing the operating system, applications, files, configuration and settings
2. The .xml configuration file associated with the .vhd containing the virtual machine settings
3. The .avhd file snapshots associated with the .vhd
While running a VM in Hyper-V, it is likely that you are also using all of the associated files (assuming, of course, that you are using snapshots). That said, it is important to understand that each virtual machine in Hyper-V has an association with its Hyper-V host: A GUID, which is how it is known and recognized on the Hyper-V host. And, because of the combination of files used and the association with the Hyper-V host, it is impossible to simply cut, copy and paste the .vhd file to transport it for use on another Hyper-V host, operations you probably performed on your old Virtual PC-based .vhd files.
Running a VM in Hyper-V calls for a more holistic approach. It’s an approach that includes all of the files. In addition, it is also necessary at this time to take care of any association challenges with the Hyper-V host. This is where the Export tool comes in to play.
When you make an export of a Hyper-V VM you get all of the files associated with the VM and a nice .xml configuration file that has been converted to an .exp file. This way, it can be Imported (read re-associated) to a different Hyper-V host. Essentially, you are creating a fully functional clone of your VM.