Western Digital WD Purple 4TB 3.5' Surveillance HDD 5400RPM 64MB SATA3 6Gb/s 150MB/s 180TBW 24x7 64 Cameras AV NVR DVR 1.5mil MTBF 3yrs - Key Features - Storage Capacity: 4 TBBuffer: 256 MBWireless LAN: No - Drive Interface: SATADrive Interface Standard: SATA/600Drive Type: Internal - Form Factor: 3.5'WD Purple - WD Purple drives are engineered specifically for surveillance to help withstand theelevated heat fluctuations and equipment vibrations within NVR environments. Anaverage desktop drive is built to run for only short intervals, not the harsh 24/7 always-onenvironment of a high-definition surveillance system. With WD Purple, you get reliable,surveillance-class storage thats tested for compatibility in a wide range of securitysystems. Exclusive All - Frame technology helps reduce frame loss and improve overallvideo playback.