modified SLDC algorithm using a larger history buffer, are advertised as having a "2.5:1" ratio. This is inferior to slower algorithms such as gzip, but similar to lzop and the high speed algorithms built into other tape drives. The actually achievable ratio generally depends on the compressibility of the data, e.g. for precompressed data such as ZIP files, JPEG images, and MPEG video or audio the ratio will be close to or equal to 1:1. WORM New for LTO-3 was write once read many (WORM) capability. This is useful for legal record keeping, and for protection from accidental or intentional erasure, for example from ransomware, or simply human error. An LTO-3 or later drive will not erase or overwrite data on a WORM cartridge, but will read it. A WORM cartridge is identical to a normal tape cartridge of the same generation with the following exceptions: the cartridge memory identifies it to the drive as WORM, the servo tracks are slightly different to allow verification that data has not been modified, the bottom half of the cartridge shell is gray, and it may come with tamper-proof screws. WORM-capable drives immediately recognize WORM cartridges and include a unique WORM ID with every dataset written to the tape. There is nothing different about the tape medium in a WORM cartridge. Encryption The LTO-4 specification added a feature to allow LTO-4 drives to encrypt data before it is written to tape. All LTO-4 drives must be aware of encrypted tapes, but are not required to support the encryption process. All current LTO manufacturers support encryption natively enabled in the tape drives using Application Managed Encryption (AME). The algorithm used by LTO-4 is AES-GCM, which is an authenticated, symmetric block cipher. The same key is used to encrypt and decrypt data, and the algorithm can detect tampering with the data. Tape drives, tape libraries, and backup software can request and exchange encryption keys using either proprietary protocols, or an open standard like OASIS's Key Management Interoperability Protocol. Partitioning The LTO-5 specification introduced the partitioning feature that allows a tape to be divided into two separately writable areas, known as partitions. LTO-6 extends the specification to allow 4 separate partitions. The Linear Tape File System (LTFS) is a self-describing tape format and file system made possible by the partition feature. File data and filesystem metadata are stored in separate partitions on the tape. The metadata,