LTO or Linear Tape Open is a magnetic tape data media. There were two forms of LTOs: Accelis and Ultrium. The Accelis form of LTO tapes was developed in 1997 for fast data access. However the LTO Accelis tape never exceeded the LTO Ultrium tape performance The LTO form Ultrium is a half-inch magnetic tape with a single reel (contrasting with the 8mm double reel Accelis). The Ultrium was developed as a drop-in replacement for the DLT . LTO Ultrium tape uses a single reel to maximize storage capacity and thus is better suited for archival use. The LTO Ultrium is very popular and “LTO” in common usage usually refers to the LTO Ultrium as the LTO Accelis are no longer commercially available.