SED means that instead of relying on the host processor and software for full-disk encryption (FDE), the encryption is done purely by the drive itself using Trusted Computing Group's (TCG) Opal standard. The Opal standard offers two major benefits over software based disk encryption: performance and security.
Every X300s includes a license for Wave's EMBASSY Security Center (ESC), which normally retails for $40. ESC can be acquired from SanDisk's SSD Dashboard under the Tools tab. ESC provides local SED management, and for IT administrators Wave offers EMBASSY Remote Administrator Server (ERAS) that allows central management of all SEDs in the organization.