Disk encryption is a special case of data at rest protection when the storage media is a sector-addressable device (e.g., a hard disk or a flash card). Disk encryption has many facets:

Disk encryption theory provides cryptographic definition of the problem and explains techniques used to solve it: ESSIV, LRW, XEX, XTS, CMC, EME, et cetera.

Encryption layer in storage stack discusses the place of an encryption layer in the solution stack of hardware and software that implements computer storage. It explains what is the difference between full disk encryption, encryption of some partitions on a disk, encrypted containers stored in regular file system, and filesystem-level encryption.

Disk encryption software discusses software packages devoted to disk encryption.

Disk encryption hardware discusses hardware.