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helical scan

The helical scan method is a recording method for tape drives and video recorders. There is also the longitudinal track method, which is also used in backup drives, and the cross-track method. All methods aim to utilize the magnetic tapes with the highest possible storage capacity and also to achieve the highest possible data transfer rate.

According to the methods, the magnetic layer of the magnetic tape is scanned with the highest possible speed of the magnetic heads. The relative speed between the magnetic tape and the magnetic head can be provided by the running speed of the magnetic tape or by a track extension on the magnetic tape. Such a track extension is used by the helical scan method, also called helical scan method, by using several rotating read/write heads. These rotating magnetic heads are located in a head drum around which the magnetic tape is wrapped.

Magnetic tape wrapped around the head drum

Magnetic tape wrapped around the head drum

Since the magnetic tape wraps around the head drum at a certain angle of inclination, but the heads rotate in a plane, and much faster than the tape speed, oblique recording tracks are produced. The wrap angle can range from 90° to over 200° and the speed of the read/write heads at several thousand revolutions per minute. With this enormously high relative speed between magnetic tape and read/write head, a high recording density and speed is achieved. In the case of data storage using the helical-scan method, the recorded data is read out by a downstream read head and error correction is performed.

Head drum in which the rotating read/write heads are located, photo; Qualstar.

Head drum in which the rotating read/write heads are located, photo; Qualstar.

Most tape drives use a head drum containing two pairs of read/write heads, but there are also methods, such as Digital Tape Format( DTF), that use eight read/write heads.

Digital Audio Tape( DAT), Digital Data Storage( DDS) and Digital Tape Format (DTF) tape drives use the helical-scan method of recording; Quarter Inch Cartridge( QIC) can also use this method.

Informations:
Englisch: helical scan
Updated at: 18.01.2005
#Words: 333
Links: method, video, longitudinal track method, backup, capacity (C)
Translations: DE
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