Tape drive

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DDS tape drive. Above, from left to right: DDS-4 tape (20 GB), 112m Data8 tape (2.5 GB), QIC DC-6250 tape (250 MB), and a 3.5" floppy disk (1.44 MB).

A tape drive, also known as a streamer, is a data storage device that reads and writes data stored on a magnetic tape or a punched tape. It is typically used for archival storage of data stored on hard drives. Tape media generally has a favorable unit cost and long archival stability.

Instead of allowing random-access to data as hard disk drives do, tape drives only allow for sequential-access of data. A hard disk drive can move its read/write heads to any random part of the disk platters in a very short amount of time, but a tape drive must spend a considerable amount of time winding tape between reels to read any one particular piece of data. As a result, tape drives have very slow average seek times. Despite the slow seek time, tapes drives can stream data to tape very quickly. For example, modern LTO drives can reach continuous data transfer rates of up to 80 MB/s, which is as fast as most 10,000 rpm hard disks.

An external QIC tape drive.

Tape drives can be connected to a computer with SCSI (most common), Fibre Channel, FICON, ESCON, parallel port, IDE, USB, FireWire or other interfaces. Tape drives can range in capacity from a few megabytes to upwards of 800 GB. Tape drive storage is usually referred to with the assumption of 2:1 compression ratio, so a tape drive might be known as 80/160, meaning that the standard storage capacity is 80 whilst the compressed storage capacity can be up to 160. The raw storage capacity is known as the native capacity.

Tape drives can be found inside autoloaders and tape libraries which assist in loading, unloading and storing multiple tapes to further increase archive capacity.

In the 1980s some forms of tape drives were used as inexpensive alternatives to disk drives, examples include the ZX Microdrive and Rotronics Wafadrive.

[edit] Shoe-shining effect

The shoe-shining effect occurs during a tape backup process when the transfer rate of the data falls below the transfer speed of the tape drive. When this occurs, the data buffer of the tape drive empties and the drive must stop, reverse position and begin writing once the tape buffer fills again.

Shoe-shining can significantly affect the attainable backup speed and place undue stress on the tape medium itself.

[edit] Advancements in the history of tape drives

Advancements in linear tape drives
Year	Manufacturer	Model	Advancements
1951	Remington Rand	UNISERVO	First tape drive
1958	IBM	729	Separate read/write heads providing transparent read-after-write verification [1]
1972	3M	QIC-11	Tape cassette (with two reels)
1974	IBM	3850	Tape cartridge (with single reel) First tape library with robotic access. [2]
1980	Cipher	(F880?)	RAM buffer to mask start-stop delays [3] [4]
1984	IBM	3480	Internal takeup reel with automatic tape takeup mechanism. Thin-film MR (magneto-resitive) head. [5]
1984	DEC	TK50	Linear serpentine recording [6]
1986	IBM	3480	Hardware data compression (IDRC algorithm) [7]
1993	DEC	Tx87	Tape directory (database with first tapemark nr on each serpentine pass). [8]
1995	IBM	3570	Head assembly that follows pre-recorded tape servo tracks (Time Based Servoing or TBS) [9] Tape on unload rewound to the midpoint - halving access time (requires two-reel cassette, resulting in lesser capacity) [10]
1997	IBM	VTS	Virtual tape - disk cache that emulates tape drive [11]
2006	StorageTek	T10000	Multiple head assemblies and servos per drive. [12]

Advancements in helical tape drives
Year	Manufacturer	Model	Advancements
1987	Exabyte/Sony	EXB-8200	First helical digital tape drive. Elimination of the capstan and pinch-roller system.
1996	HP	DDS3	PRML Partial Response Maximum Likelihood reading method (no fixed thresholds) [13]
1999	Exabyte	Mammoth-2	The small cloth-covered wheel auto-cleaning tape heads (Dynamic Head Cleaner). Inactive burnishing heads to prep the tape and deflect any debris or excess lubricant. Section of cleaning material at the beginning of each data tape.
2003	Sony	SAIT-1	Single-reel cartridge for helical recording

[edit] References

This article was originally based on material from the Free On-line Dictionary of Computing, which is licensed under the GFDL.

view • talk • edit	Magnetic tape data storage formats
	Linear	Helical-Scan
Three Quarter Inch (~19 mm)	LINCtape (1962) - DECtape (1963)	Sony DIR (19xx) - Ampex DST (1992)
Half Inch (12.65 mm)	UNISERVO (1951) - IBM 7 Track (1952) - 9 Track (1964) - IBM 3480 (1984) - DLT (1984) - IBM 3590 (1995) - T9840 (1998) - T9940 (2000) - LTO Ultrium (2000) - T10000 (2006)	Redwood SD-3 (1995) - DTF (19xx) - SAIT (2003)
Eight Millimeter (8 mm)	Travan (1995) - IBM 3570 MP (1997)	Data8 (1987) - Mammoth (1994) - AIT (1996) - VXA (1999)
Quarter Inch (6.35 mm)	QIC (1972) - SLR (1986) - Ditto (1992)
Eighth Inch (3.81 mm)	KC Standard, Compact Cassette (1975) - DC100 (1976) - Datassette (1977) - DECtapeII (1979)	DDS/DAT (1989)
Stringy (1.58 - 1.9 mm)	Exatron Stringy Floppy (1979) - ZX Microdrive (1983) - Rotronics Wafadrive (1984)