Also known as: LTO Ultrium, Ultrium
The open tape cartridge standard used by IBM's tape libraries and autoloaders, currently on its 10th generation (LTO-10, 40 TB native per cartridge).
LTO, short for Linear Tape-Open, is the open (multi-vendor) magnetic tape standard behind essentially every enterprise tape library sold today, including IBM's TS4300, TS4500, and TS2900 lines. It was developed jointly by IBM, HPE, and Quantum specifically so tape media and drives from different manufacturers stay interoperable, unlike the closed, single-vendor tape formats it replaced.
Each LTO generation roughly doubles native cartridge capacity over the last. As of 2026 the current generation is LTO-10, at 40 TB native (up to 100 TB at 2.5:1 compression) per cartridge and 400 MBps native transfer speed. LTO-9, the prior generation, holds 18 TB native.
Generation compatibility is the detail that actually matters when buying a drive or library: from LTO-8 onward, a drive normally reads and writes its own generation and the one directly before it, and can read (but not write) two generations back. LTO-10 breaks that pattern: it introduced a new format that is not backward compatible with LTO-9 media at all, so an LTO-10 drive cannot read existing LTO-9 tapes. Anyone with an existing LTO-9 tape library planning an LTO-10 upgrade needs to plan for that gap specifically, not assume the usual one-generation overlap applies. See the full LTO Generation Guide for the generation-by-generation capacity and compatibility table.