A Digital Video Recorder (DVR) is the legacy appliance that records analog cameras. Analog cameras send a continuous analog video signal over coax cable; the DVR digitises that signal, compresses it, and stores it to disk. In the IP era the DVR is the predecessor of the NVR — same job (record and play back), different input (analog coax instead of a network stream).
DVRs did not vanish with the arrival of IP. "HD-over-coax" formats — HD-TVI, HD-CVI, and AHD — push megapixel resolution down existing coax to a compatible DVR, which lets a site upgrade image quality without rewiring. That is why many older buildings still run a DVR: the coax is already in the walls.
The trade-offs are the reason new systems go IP. Analog plant means one cable per camera back to the DVR, resolution and analytics options well behind modern IP cameras, and no native on-camera intelligence. A DVR is a sensible way to keep an existing analog estate alive; it is rarely the right foundation for a new deployment, where IP cameras, PoE, and a VMS or NVR give more resolution, less cabling, and a path to analytics.
