The hard drive in a PVR (= 'personal video recorder'), or in a combined DVD recorder & PVR, works in the same way as the hard drive in your computer. It's stores data (i.e. video recordings) on rotating discs so that you can call up that data (i.e. play the video recordings) simply by pressing a few buttons.
This well-reviewed (combined) recorder allows you to store video recordings on the hard drive and play them back from there. It also allows you to copy recordings from the hard drive to DVD+RW discs (as well as to other DVD formats) but you can't record
directly to discs:
https://tinyurl.com/yd67stzm
The user manual is here, so you can see how it works:
https://tinyurl.com/y8r74uey