particular generation of LTO technology and cannot be used in any other way (with the exception of LTO-M8, see below). While Ultrium drives are also defined by a particular generation, they are required to have some level of compatibility with older generations of cartridges. The rules for compatibility between generations of drives and cartridges are as follows: Up to and including LTO-7, an Ultrium drive can read data from a cartridge in its own generation and the two prior generations. LTO-8 drives can read LTO-7 and LTO-8 tape, but not LTO-6 tape. An Ultrium drive can write data to a cartridge in its own generation and to a cartridge from the one prior generation in the prior generation's format. Some LTO-8 drives may write previously unused LTO-7 tapes with an increased, uncompressed capacity of 9 TB (Type M (M8)). Only new, unused LTO-7 cartridges may be initialized as LTO-7 Type M. Once a cartridge is initialized as Type M it may not be changed back to a 6 TB LTO-7 cartridge. LTO-7 Type M cartridges are only initialized to Type M in an LTO-8 drive. LTO-7 drives are not capable of reading LTO-7 Type M cartridges. An Ultrium drive cannot make any use of a cartridge from a more recent generation. For example, an LTO-2 cartridge can never be used by an LTO-1 drive and even though it can be used in an LTO-3 drive, it performs as if it were in an LTO-2 drive. Within the compatibility rules stated above, drives and cartridges from different vendors are expected to be interchangeable. For example, a tape written on any one vendor's drive should be fully readable on any other vendor's drive that is compatible with that generation of LTO. Core technology Tape specifications Physical structure LTO Ultrium tape is laid out with four wide data bands sandwiched between five narrow servo bands. The tape head assembly, that reads from and writes to the tape, straddles a single data band and the two adjacent servo bands. The tape head has 8, 16, or 32 data read/write head elements and 2 servo read elements. The set of 8, 16, or 32 tracks are read or written in a single, one-way, end-to-end pass that is called a "wrap". The tape head shifts laterally to access the different wraps within each band and also to access the other bands. Writing to a blank tape