The Digital Linear Tape (DLT) is an old and venerable tape format dating back many years. Back in the day, a cartridge held about 2.6GB native. Stretching my mind back, it seems like the first time I saw one of these was on a DecStation, but they called it a TK50, which doesn't seem right, except I'm almost positive the form factor was the same. Who knows.

Basically these are 1/2 inch multi-track metal particle tapes in a square plastic cartridge of about the thickness of a VHS casette and half the width. Of many available types, there's DLT III (10 GB), DLT IIIXT (15 GB), and DLT IV (20, 35, 40 GB) - all sizes native uncompressed. Tracks are stacked densely in a configuration called Linear Serpentine Recording. The modern tapes (IIIXT and above) are certified for up to 1 million passes, and rated for a 30 year shelf life. Not bad. The format was invented and is still owned and licenced by Quantum, although there are a number of open standards describing the technologies used.

DLT has tended to be more expensive than the alternatives, with drives often costing hundreds or thousands more than comparable DAT models, a more recent arrival on the backup drive market, and media going for over $70 per tape. However, DLTs are in wide and common use, especially at sites which have been operating since before there was a decent alternative in the size and price range served by these systems (read: unix/other mainframe ops). It's also considered to be more reliable and durable a backup solution than the prevailing alternatives (which in addition to DAT/AIT, include Exabyte and Travan); perhaps deservedly. It's what admins like to call "mature."