The Western Digital Red NASware 3.0 WD40EFRX is a 4TB internal desktop hard drive with a 3.5-inch form factor. It has a SATA III interface and a 64MB cache. This NAS hard drive is suitable for use in network-attached storage devices. It is designed to operate 24/7 and has a rotation speed of 5400 RPM. The hard drive is compatible with HDD drive types and supports HDD storage format.