Western Digital WD5002ABYS RE3 3.5-inch Enterprise SATA Hard Drive (500 GB, 1.2 million hours MTBF, 16 MB Cache, 7200 RPM) Reliability features makes them the perfect Solution for servers, video surveillance, and other demanding write-intensive applications Dual processors provide twice the processing power Thermal extended burn-in tested Time-limited error recovery (TLER) - Prevents drive fallout caused by the extended hard drive error-recovery WD RE3 7200 RPM Enterprise SATA hard drives are packed with performance and reliability features making them the perfect solution for servers, video surveillance, and other demanding write-intensive applications. Reliability features makes them the perfect Solution for servers, video surveillance, and other demanding write-intensive applications Dual processors provide twice the processing power Thermal extended burn-in tested Time-limited error recovery (TLER) - Prevents drive fallout caused by the extended hard drive error-recovery