Dahua 5 Series 16 Channel 4K 2 HDD NVR (DHI-NVR5216-4KS2(V2.0)) - Main Processor: Industrial embedded micro-processor, Resolution: 12MP, 8MP, 6MP, 5MP, 4MP, 3MP, 1080p, 1.3MP, 720p, D1, and more, Access Channel: 16, Storage Method: Local HDD and network, External Ports: Audio Input: 1 channel, RCA connector, Audio Output: 1 channel, RCA connector, which supports voice intercom output, HDD: 2 SATA III ports, up to 10 TB for a single HDD. The maximum HDD capacity varies with environment temperature, Alarm Input: 4 channels, Alarm Output: 2 channels, RS-232: 1 channel, used to debug and pass through serial data, RS-485: 1 channel, used to control PTZ, and it supports multiple protocols, USB: 1 front USB 2.0 port, 1 rear USB 3.0 port, 1 x HDMI, 1 x VGA, Network: 1 RJ-45 10/100/1000 Mbps self-adaptive Ethernet port, OS: Embedded Linux