This article is from the storage FAQ part2, by Rodney D. Van Meter with numerous contributions by others.
Spectra Logic makes SCSI-controlled 8mm and 4mm (DAT) autochangers. One to four drives, with 20 to 60 slots. Capacity currently up to 600 GB of DDS-2 (4mm) or 300 GB 8mm. Early models (STL-6000 & STL-8000) were a rotating carousel. Newer ones use an arm and the tapes don't move. Supported by a variety of software vendors. List prices of $9K (Spectra 4000/20 slots, one DDS-2 drive) to $31K (60 slots with four drives and barcode support) including drives. They also make a thing called TapeFrame, which consists of several of their autochangers working in conjunction, with capacities up to 2.2 TB. U.S.: 1-800-833-1132 or 303-449-6400 (Britt Terry, firstname.lastname@example.org, 95/1/12) See also under backup software, and on the web at http://www.spectralogic.com.