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A tape drive is a data storage device that reads and writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and a long archival stability. A tape drive provides sequential access storage, unlike a hard disk drive, which provides random access storage. A disk drive can move to any position on the disk in a few milliseconds, but a tape drive must physically wind tape between reels to read any one particular piece of data. As a result, tape drives have very slow average seek times to data. However, tape drives can stream data very quickly off the tape when it hits the right position. For example, Linear Tape-Open (LTO) supported continuous data transfer rates of up to 140 MB/s, comparable to hard disk drives. == Design == Magnetic tape drives were first used for data storage on mainframe computers in the 1950s, with capacities less than one megabyte. As technology advanced, capacities increased to 10 terabytes or higher of uncompressed data per cartridge . In early computer systems, magnetic tape might be the main storage medium; although the drives were expensive, the tapes were inexpensive. Some computer systems ran the operating system on tape drives such as the DECtape drive; DECtape had fixed-size indexed blocks that could be rewritten without disturbing other blocks, so DECtape could be used like a slow disk drive. As some data can be compressed to a smaller size than the files on hard disk, it has become commonplace when marketing tape drives to state the capacity with the assumption of a 2:1 compression ratio; thus a tape with a capacity of 80 GB would be sold as "80/160". The true storage capacity is also known as the native capacity or the raw capacity. IBM and Sony have also used higher compression ratios in their marketing materials. The compression ratio actually achievable depends on the data being compressed. Some data has little redundancy; large video files, for example, already use compression technology and cannot be compressed further. A sparse database, on the other hand, may allow compression ratios better than 10:1. Tape drives can be connected to a computer with SCSI (most common), Fibre Channel, SATA, USB, FireWire, FICON, or other〔Historical interfaces include also ESCON, parallel port, IDE, Pertec.〕 interfaces. Tape drives are used with autoloaders and tape libraries which automatically load, unload, and store multiple tapes, increasing the volume of data which can be stored without manual intervention. In the early days of home computing floppy and hard disk drives were very expensive. Many computers had an interface to store data via an audio tape recorder, typically on Compact Cassettes. Simple dedicated tape drives, such as the professional DECtape and the home ZX Microdrive and Rotronics Wafadrive, were also designed for inexpensive data storage. However, the drop in disk drive prices made such alternatives obsolete. True data tape drives used more advanced techniques such as multilevel forward error correction, shingling, and linear serpentine layout for writing data to tape, 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Tape drive」の詳細全文を読む スポンサード リンク
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