Linear Tape-Open (LTO), also known as the LTO Ultrium format, is a magnetic tape data storage technology used for backup, data archiving, and data transfer. It was originally developed in the late 1990s as an open-standard alternative to the proprietary magnetic tape formats available at the time. Upon introduction, LTO rapidly defined the super tape market segment and has consistently been the best-selling super-tape format. The latest generation as of 2026, LTO-10, defines two unique cartridge types which can hold or each.
Cartridges (a.k.a. tapes) contain hundreds of meters of half-inch (12.65 mm) wide tape media wound onto a single reel. The first generation LTO cartridge was released in 2000 and stored of data. With each new generation, the capacity has increased. All Ultrium cartridges are the same physical size and shape.
Mechanisms (a.k.a. drives, streamers, transports) extract the tape from the cartridge and spool it up on a second reel in the mechanism, reading or writing data as the tape moves between reels. Robotic libraries exist that can hold hundreds or thousands of LTO cartridges and dozens of mechanisms.
Compared to disk or flash storage, LTO offers high-capacity removable cartridges with a lower cost per TB and better long term stability. When considering a complete storage system, LTO requires significantly less electrical power per TB. It also includes built-in technologies useful for data sharing and safe-keeping, like LTFS, WORM, encryption and data compression.
Historical context
Half-inch (12.65 mm) wide magnetic tape has been used for data storage since the 1950s, starting with the open reel formats IBM 7-track and later IBM 9-track.
In the mid-1980s, smaller, enclosed, single-reel cartridge formats were developed by IBM and DEC. Although the physical tape was nominally the same width in these new formats and the preceding open-reel formats, the technologies and intended markets were significantly different and there was no compatibility between them. The IBM 3480 tape format was designed to meet the demanding requirements of its mainframe products. DEC's CompacTape was targeted at a broader market, including minicomputers and smaller systems. Later on, it was renamed Digital Linear Tape (DLT) and eventually sold to Quantum Corporation.
In the late 1980s, Exabyte's Data8 format, derived from Sony's dual-reel cartridge 8 mm video format, saw some popularity, especially with UNIX systems. Sony followed this success with their own now-discontinued 8 mm data format, Advanced Intelligent Tape (AIT).
By the late 1990s, Quantum's DLT and Sony's AIT were the leading options for high-capacity tape storage for PC servers and UNIX systems. These technologies were tightly controlled by their owners and consequently, there was little to no competition between vendors and the prices were relatively high.
Birth of LTO Seeing an opportunity, IBM, HP and Seagate formed the LTO Consortium, which introduced a more open format focusing on the same mid-range market segment. Much of the technology is an extension of the work done by IBM at its Tucson lab during the previous 20 years.
In 2000, and around the time of the release of LTO-1, Seagate's magnetic tape division was spun off as Seagate Removable Storage Solutions, renamed Certance in 2003, and subsequently acquired by Quantum in 2004.
Unrealized variations Initial plans called for two distinct LTO formats: 1) Ultrium - with half-inch tape on a single reel, optimized for high capacity, and 2) Accelis - with 8 mm tape on dual reels, optimized for fast access. Only Ultrium was ever produced, so in common usage, LTO refers to just the Ultrium form factor.
Additionally, the first generation of Ultrium was proposed to be available with 4 different lengths of tape, holding 10 GB, 30 GB, 50 GB, and 100 GB per cartridge. Only full length cartridges were ever produced.
Generations
As of 2026, ten generations of LTO Ultrium technology have been made available and four more are planned. Between generations, there are strict compatibility rules that describe how and which drives and cartridges can be used together.
The LTO Consortium publishes a roadmap of future generations, which states that LTO-14 will have a capacity of "up to" 913 TB compressed (365 TB native).
Key specifications Format LTO-1 LTO-2 LTO-3 LTO-4 LTO-5 LTO-6 LTO-7 Type M Type M (label id: M8) is an alternate format of an LTO-7 cartridge, not an independent generation. See: Compatibility LTO-8 LTO-9 LTO-10 Release date 2000 2003 2005 2007 2010 Dec. 2012 Dec. 2015 Dec. 2017 Sep. 2021 May 2025 Jan. 2026Native capacity (uncompressed)The units for data capacity and data transfer rates generally follow the "decimal" SI prefix convention (e.g. mega = 106), not the binary interpretation of a decimal prefix (e.g. mega = 220). 100 GB 200 GB 400 GB 800 GB 1.5 TB 2.5 TB 6.0 TB 9 TB 12 TB 18 TB 30 TB 40 TB Advertised capacity (compressed)On packaging and in marketing materials, capacities are often stated assuming that data will be compressed at a fixed ratio, commonly 2:1 or 2.5:1. 200 GB 400 GB 800 GB 1.6 TB 3.0 TB 6.25 TB 15 TB 22.5 TB 30 TB 45 TB 75 TB 100 TB Max speed MB/s (uncompressed)This is the maximum data transfer rate between the drive and the tape. See: Data transfer rates 20 40 80 120 140 160 300 360 400 Compression capable? colspan="5" (2:1) colspan="7" (2.5:1) WORM capable? colspan="2" colspan="5" colspan="4" Encryption capable? colspan="3" colspan="9" LTFS capable? colspan="4" colspan="8" Max. number of partitions 1 (no partitioning) 2 4
Compatibility In contrast to other tape technologies, an Ultrium cartridge is rigidly defined by a particular generation of LTO technology and cannot be used in any other way (with the exception of LTO-7 Type M, see below). Ultrium drives prior to LTO-10LTO-10 Breaks the Mold: New Tape Format Sacrifices Compatibility have some level of compatibility with older generations of cartridges.
Compatibility Drives LTO-1 LTO-2 LTO-3 LTO-4 LTO-5 LTO-6 LTO-7 LTO-8 LTO-9 LTO-10 LTO-1 0.1 TB L1 -- align="center" align="center" align="center" LTO-2 0.2 TB L2 -- align="center" align="center" align="center" LTO-3 0.4 TB L3 LT align="center" align="center" align="center" LTO-4 0.8 TB L4 LU align="center" align="center" align="center" LTO-5 1.5 TB L5 LV align="center" align="center" align="center" LTO-6 2.5 TB L6 LW align="center" align="center" LTO-7 6 TB L7 LX align="center" align="center" LTO-7 Type M 9 TB M8 -- align="center" LTO-8 12 TB L8 LY align="center" align="center" LTO-9 18 TB L9 LZ align="center" LTO-10 30 TB LA LH align="center" 40 TB PA align="center" Generation Capacity RegularID WORMID
The rules for compatibility between generations of drives and cartridges are as follows:
Drives of every generation can read and write cartridges of the same generation. Drives from generations 2 through 9 can also read and write cartridges of the prior generation. Drives from generations 3 through 7 can also read (but not write) cartridges of 2 generations prior. Drives from generation 8 can reformat unused cartridges from generation 7 with a special, higher-capacity format (Type M (M8)). Once reformatted as Type M, the cartridge is only compatible with drives from generation 8.
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
Generations LTO-1 LTO-2 LTO-3 LTO-4 LTO-5 LTO-6 LTO-7 LTO-7 Type M (M8) LTO-8 LTO-9 LTO-10 Native capacity 100 GB 200 GB 400 GB 800 GB 1.5 TB 2.5 TB 6.0 TB 9.0 TB 12 TB 18 TB 30 TB 40 TB Tape length 609 m 680 m 820 m 846 m 960 m 1035 m 1337 m Tape width 12.650 mm ± 0.006 mm Tape thickness 8.9 μm 8 μm 6.6 μm 6.4 μm 6.4 μm or 6.1 μm (BaFe) 5.6 μm 5.2 μm 4.0 μm Magnetic pigment material Metal particulate (MP) MP or BaFe BaFe SrFe & BaFe hybrid Base material Polyethylene naphthalate (PEN) AramidTape keeps kicking, 'breakthrough' 40TB native spec announced — LTO-10 tapes claim up to 100TB compressed data capacity, hold 2.2X more data than previous spec Data bands per tape4 Wraps per band 12 16 11 14 20 34 28 42 52 70 118 Tracks per wrap, read/write elements 8 16 32 Total tracks 384 512 704 896 1,280 2,176 3,584 5,376 6,656 8,960 15,104 Linear density (bits/mm) 4,880 7,398 9,638 13,250 15,142 15,143 19,094 19,104 20,668 21,459 Time to write a full tape at max speed (hh:mm) 1:23 1:51 3:10 4:20 5:33 8:20 9:16 12:30 20:50 Encoding RLL 1,7 RLL 0,13/11; PRML RLL 32/33; PRML RLL 32/33; NPML End-to-end passes required to fill tape 48 64 44 56 80 136 112 168 208 280 472 Expected tape durability, end-to-end passes 9,600 16,000 16,000 11,200 16,000 20,000
Band layout
LTO Ultrium tape is laid out with four wide data bands sandwiched between five narrow servo bands. A thin edge guard band runs along each edge. The tape head assembly, which reads from and writes to the tape, straddles a single data band and the two adjacent servo bands. The head assembly has two servo read heads, separated by multiple (8, 16, or 32) data read and write heads, evenly spaced across the data band.
Servo bands
The servo bands contain a pattern of angled magnetic stripes permanently written to the tape at the factory. The primary use of the servo signal is to maintain the transverse position of the tape head in relation to the tape. This allows the tape head to precisely follow each track as the tape moves past at high speed.
The servo signal can also encode a low bitrate data stream. This data is used to encode the longitudinal position (LPOS) of that point on the tape. In addition to LPOS, manufacturers can encode additional data in the signal. With LPOS and a precise time source, a tape drive can precisely measure the velocity of the tape.
The incompatibility between LTO-10 and earlier generations is due to two changes to the servo positioning system. First, the angle of the magnetic stripes was changed from 6° in all previous generations to 36° for better head-positioning accuracy. Second, the head assembly is tilted, allowing it to follow each servo band independently (adjusting the tilt angle to follow any change in the servo band spacing), thereby correcting for any variation in tape width due to temperature, humidity, tension, etc.
Data bands The actual data stored on the tape is recorded in individual tracks located within the data bands. Depending on the generation, there could be from 96 to almost 4000 data tracks per band.
The tape head has 8, 16, or 32 data read/write head elements and additional servo read elements. The heads read or write tracks in parallel, each within its own data sub-band. The set of 8, 16, or 32 tracks written in a single, one-way, end-to-end pass 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 starts at band 0, wrap 0, a forward wrap that runs from the beginning of the tape (BOT) to the end of the tape (EOT) and includes a track that runs along one side of the data band. The next wrap written, band 0, wrap 1, is a reverse wrap (EOT to BOT) and includes a track along the other side of the band. Wraps continue in forward and reverse passes, with slight shifts toward the middle of the band on each pass.
Because each data head only needs to be positioned within one half (upper or lower, depending on tape direction) of its data sub-band, and there are at least 8 heads, the servo bands only need to be slightly more than the width of the data bands.