Tape Storage
In addition to the storage of data on a computer's hard drive or on a server, the storage of a copy of the data on a removable media is prudent strategy. In the event of the computer's failure or destruction, the data is safe for subsequent retrieval and use.
Prior to the development of solid data storage, such as CD- and DVD-ROM, the use of tape as a storage medium was widespread. Tape has always been the least expensive storage medium at less than a penny per megabyte, versus five cents for optical or magnetic storage. Tape storage, however, acquired the reputation of being very slow. Now, faster and more efficient tape technologies are available from a number of companies. If the time required for backup is not a factor, tape storage can still be the best option for a user.
The most popular tape devices for smaller commercial users are those based on the digital audio tape (DAT) format. DAT devices are grouped under another specification called digital data storage (DDS). Some DDS devices can hold up to 24 GB of compressed data. Other tape products offer more storage capacity. The Advanced Intelligent Tape (AIT) is a magnetic tape that uses 8-mm cassettes with built-in memory chips to speed the process of data retrieval. Another magnetic tape technology, digital linear tape (DLT), can hold up to 70 GB of data. Finally, 8-mm tape, named for its width, was first introduced in 1987. Improvements in the ensuing years have boosted its storage capacity to 40 GB.
With DLT, the data recording process involves the routing of the tape out of the cassette, around the rotating read/write drum assembly, and finally back into the cassette.
Data can be written onto DLT and other tapes in several ways. In linear recording, the data track goes the entire length of the tape (about 1,800 feet). When the end of the tape is reached, the heads are repositioned and the tape runs back the other way, recording the entire length. This pattern continues until the tape is full. In a newer modification, the head assembly can be rotated three ways during the back-and-forth motion to create a highly condensed herringbone pattern of data. By contrast, the helical scan method, used in the AIT for example, writes data to the tape in diagonal stripes running across the tape. The angled position allows the storage of more information per area of tape.
Among the new tape storage products, which debuted in the past several years, the most prominent is called Linear Tape Open (LTO). The first generation LTO drives can store 200 GB of compressed data per tape. By the fourth generation, it is anticipated that the storage capacity could reach 1.6 TB of compressed data. Researchers are also exploring the use of a brand of ordinary commercial adhesive tape as a storage medium. The structure of the tape may be suited to the holographic storage of data.
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