Amazon.com: Western Digital 4TB WD Purple Surveillance Internal Hard Drive HDD - SATA 6 Gb/s, 256 MB Cache, 3.5" - WD42PURZ : Electronics
WD Purple 4TB Surveillance Hard Disk Drive - 5400 RPM Class SATA 6 Gb/s 64MB Cache 3.5 Inch - WD40PURZ - Walmart.com
Amazon.com: WD Purple NV 4TB Surveillance Hard Disk Drive - Intellipower SATA 6 Gb/s 64MB Cache 3.5 Inch - WD4NPURX : Electronics
Seagate 4TB SkyHawk SATA III 3.5" Internal HDD ST4000VX007 B&H
Amazon.com: Western Digital Purple 4TB Surveillance Hard Disk Drive - 5400 RPM Class SATA 6 Gb/s 64MB Cache 3.5 Inch - Western Digital40PURZ [Old Version] : Electronics
Amazon.com: WD Purple 4 TB Surveillance Hard Disk Drive, Intellipower 3.5 Inch SATA 6 Gb/s 64 MB Cache 5400 RPM : Electronics
WD Purple 4TB Surveillance Hard Disk Drive 3.5" - Newegg.com
Surveillance Grade Hard Drive for your Surveillance System (1TB-20TB)