Western Digital 3TB SATA Purple Desktop Hard Disk. Western Digital purple surveillance WD30PURZ hard disk drive has 64MB cache, 3TB, 3.5" x 1/3h, 7 pin serial ATA, drive transfer rate 600 Mbps, internal data rate 145 Mbps, MTBF 1000000 hours, non-recoverable errors 10 per 10^14, advanced format technology, IntelliPower, IntelliSeek, time-limited error recovery, surveillance system compatible and AllFrame.