reel, optimized for high capacity, and Accelis with 8 mm tape on dual reels, optimized for low latency. 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, later renamed Certance, which was subsequently acquired by Quantum. Generations Despite the initial plans for two form-factors of LTO technology, only Ultrium was ever produced. The other proposed format was Accelis, developed in 1997 for fast access to data by using a two-reel cartridge that loads at the midpoint of the 8 mm wide tape to minimize access time. IBM's (short-lived) 3570 Magstar MP product pioneered this concept. The real-world performance never exceeded that of the Ultrium tape format, so there was never a demand for Accelis and no drives or media were commercially produced. As of 2008, LTO Ultrium was very popular and there were no commercially available LTO Accelis drives or media. In common usage, LTO generally refers only to the Ultrium form factor. The first generation of Ultrium tapes were going to be available with four types of cartridge, holding 10 GB, 30 GB, 50 GB, and 100 GB. Only the full length 100 GB tapes were produced. As of 2020, nine generations of LTO Ultrium technology have been made available and five more are planned. Between generations, there are strict compatibility rules that describe how and which drives and cartridges can be used together. While data capacity and speed figures vary with uncompressed or compressed data, most manufacturers list compressed capacities and speeds on their marketing material. Capacities are often stated on tapes as double the actual value, assume that data will be compressed with a 2:1 ratio (IBM uses a 3:1 compression ratio in the documentation for its mainframe tape drives. Sony uses a 2.6:1 ratio for SAIT). See Compression below for algorithm descriptions and the table above for allowable LTO compression ratios. 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). Minimum and maximum reading and writing speeds are drive-dependent. Drives usually support variable-speed operation to dynamically match the data rate flow. This nearly eliminates tape backhitching or "shoe-shining", maximizing overall throughput and device/tape life. Compatibility In contrast to other tape technologies, an Ultrium cartridge is rigidly defined by a