The WD PURPLE HDD’s technical highlight is it’s 6Gb/s interface, which is the latest SATA III standard. This drive in particular has a storage capacity of 4TB and has a massive 64MB Cache. WD Purple 4TB Surveillance Hard Drive - 5400 RPM Class, SATA 6 Gb/s, 64 MB Cache, 3.5" -.
eBay