This USB 2.0 to Dual SATA JBOD External Hard Drive Enclosure is a perfect solution for applications requiring enhanced add-on storage capacity. Supporting the latest generation of SATA hard drive storage up to 2 Terabyte (2.0 TB) capacity, the enclosure allows two 3.5in Serial ATA hard drives to be installed for a total maximum JBOD capacity of up to 4 Terabytes. The hard drives can be concatenated for operation as a single high capacity drive, or left as JBOD (still with a combined capacity limit of 3TB). The external hard drive enclosure includes a built-in 50mm fan that re-distributes the heat build-up resulting from typical drive operation. This is especially important when using large capacity hard drives (750Gb to 2TB), and faster ?spinning" drives (i.e 7200 RPM). By keeping the hard drives cooler, the enclosure maintains an ideal operating environment for the drives, which not only optimizes performance and preserves data integrity, but also helps prolong drive life span.