You can do it through the Disk Management under Control Panel. Shrink the volume (your drive C). An unallocated space will be created which you can partition as a 2nd drive.

Alternatively, you can use a 3rd party program that is easier to use:
http://www.partition-tool.com/

Either way, you won't need to reformat your hard drive C nor reinstall Windows, drivers and applications. It will be done safely on the fly without data loss and in only a few minutes.

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