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.7-track tape that could store every 6-bit byte plus a parity bitGroup coded recording for error recoveryLinear serpentine recordingFirst tape library with robotic accessThin-film magnetoresistive (MR) headElimination of the capstan and pinch-roller systemTape on unload rewound to the midpoint—halving access time (requires two-reel cassette)Inactive burnishing heads to prep the tape and deflect any debris or excess lubricantSection of cleaning material at the beginning of each data tape 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 large average access times. However, tape drives can stream data very quickly off a tape when the required position has been reached. For example, as of 2010 Linear Tape-Open (LTO) supported continuous data transfer rates of up to 140 MB/s, a rate comparable to hard disk drives. Magnetic tape drives with capacities less than one megabyte were first used for data storage on mainframe computers in the 1950s. As of 2014, capacities of 10 terabytes or higher of uncompressed data per cartridge were available. In early computer systems, magnetic tape served as the main storage medium because although the drives were expensive, the tapes were inexpensive. Some computer systems ran the operating system on tape drives such as DECtape. DECtape had fixed-size indexed blocks that could be rewritten without disturbing other blocks, so DECtape could be used like a slow disk drive. Data tape drives may use advanced data integrity techniques such as multilevel forward error correction, shingling, and linear serpentine layout for writing data to tape. Tape drives can be connected to a computer with SCSI, Fibre Channel, SATA, USB, FireWire, FICON, or other 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. As some data can be compressed to a smaller size than the original files, 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. The compression ratio actually achievable depends on the data being compressed. Some data has little redundancy; large video files, for example, already use compression and cannot be compressed further. A database with repetitive entries, on the other hand, may allow compression ratios better than 10:1. A disadvantageous effect termed shoe-shining occurs during read/write if the data transfer rate falls below the minimum threshold at which the tape drive heads were designed to transfer data to or from a continuously running tape. In this situation, the modern fast-running tape drive is unable to stop the tape instantly. Instead, the drive must decelerate and stop the tape, rewind it a short distance, restart it, position back to the point at which streaming stopped and then resume the operation. If the condition repeats, the resulting back-and-forth tape motion resembles that of shining shoes with a cloth. Shoe-shining decreases the attainable data transfer rate, drive and tape life, and tape capacity.