WD Blue 4TB Blue SATA 3.5in Internal HDDWD Purpledrives are designed to meet the challenges of 24x7 video surveillance recording. These drives are engineered specifically for surveillance to help withstand the elevated heat fluctuations and equipment vibrations within NVR environments. An average desktop drive is built to run for only short intervals, not the harsh 24 7 always on environment of a high definition surveillance system. With WD Purple drives, you get reliable, surveillance