Vacuum column (tape drive)

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 direct 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 a tape when the required position has been reached. For example, as of 2010^[update]Linear Tape-Open (LTO) supported continuous data transfer rates of up to 140 MB/s, comparable to hard disk drives.

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 as of 2014^[update]. 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.

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