4 Channel, Embedded Linux OS. True H.264 Compression. Triplex function - simultaneous record / playback / network. 1main composite, 1 spot, 1 VGA.Touch Sensitive Front Panel Interface. USB Flashdrive Backup, USB CD-RW, DVD-RW Backup. Internal HDD (SATA): 1 (Up to 1TB). 1 Ch Audio with remote Audio over network, Watermark. Watch dog / Power Failure Recovery. Firmware upgrade via USB, USB mouse controlled. RS-422/485 for PTZ speed dome and Controller Keyboard. Simultaneous users, Free DDNS Support. Remote View via iPhone, BlackBerry and Windows Mobile. Phone (Tested in US, Canada, and Korea). Optional HDD price and installation upon request.