The StorageTek 9840 was a magnetic tape system for data backup, primarily for mainframe use. The series was first introduced in 1998 with the T9840A, which had an uncompressed capacity of 20 GB. The final incarnation was the T9840D which had a capacity of 75 GB.
The StorageTek 9840 was unusual compared to its competitors such LTO and Super DLT, and to other StorageTek formats such the T10000, as the cartridges contained two reels, reducing the amount of tape that was stored in the cartridge but making loading of the tape very fast. Like many other backup tape cartridges, it used serpentine recording and ½-inch tape.
The T9840B doubled the data transfer rate of the T9840A model, making it the fastest tape drive at the time, though it was considered expensive compared to rivals, especially as its capacity was lower.
The final 9840 drives were shipped in 2009.