Western Digital WD40PURZ 4TB Purple Surveillance Grade 3.5" HDD Hard Drive Built for 24/7, always-on, high-definition security systems. With a supported workload rate of up to 180 TB/yr and support for up to 64 cameras, WD Purple drives are optimized for surveillance systems. WD Purple drives have been engineered specifically for the extreme demands of high temperature, 24/7 surveillance systems. From a worldwide leader in the storage industry, WD Purple is engineered for quality video playback when you need it most. WD Purple drives are optimized to support up to 64 cameras, giving you flexibility to upgrade or expand your security system.