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Listen to the Computerworld TechCast: Tape Types.

For almost as long as computers have existed, magnetic tape has been the backup medium of choice. Tape is inexpensive, well understood and easy to remove and replace.

But as hard drives grew larger and databases became massive data warehouses, tape had to change to store more data and do it faster. From 10-in. reels of 0.5-in. 9-track mainframe tape, focus shifted to the speed and convenience of tape cartridges.

Over the past 30 years, there have been many tape cartridge formats, and even today several formats are widely used. This QuickStudy aims to sort out differences among them and help explain which formats best suit various needs.

Linear Tape-Open (LTO)

This open-format technology was jointly developed by Hewlett-Packard Co., IBM and Seagate Removable Storage Solutions (now Certance LLC), beginning in 1997.

"Open" means that tapes and drives from different manufacturers are compatible with one another. Historically, tapes could often be read only by the drive that wrote them.

LTO uses linear, multichannel, serpentine (back-and-forth) recording on 0.5-in. tape with magnetic servo for error correction and hardware data compression. An embedded electronics module can store and retrieve usage and other information about a cartridge. LTO technology was originally announced in two variants, Accelis and Ultrium, aimed at speed and capacity, respectively. However, there was no demand for Accelis, and it has since been withdrawn.

Ultrium, a direct competitor to Super Digital Linear Tape (SDLT), uses a single tape spool inside a cartridge. The current second-generation Ultrium-2 tapes can store 200GB of data in native mode, or 400GB if compression is used. A March 2003 report by Gartner Inc. analyst Fara Yale states that more than twice as many Ultrium drives as SDLT drives were shipped in 2002.

Digital Linear Tape (DLT)

Developed by Digital Equipment Corp. in the 1980s, DLT is an adaptation of older reel-to-reel mainframe recording practice, where the removable media uses a single reel of tape and the drive handles the takeup end. According to the DLT Web site (www.dlttape.com), more than 2 million DLT drives have been sold, as well as over 90 million tape cartridges. In the most recent version, SDLT 320, optical lasers use servo tracks on the back of the tape to align the magnetic recording heads. Current SDLT drives can read older DLT media.