helical scan


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helical scan

A tape recording method that uses a spinning read/write head and diagonal tracks. Although it uses a rather complex transport mechanism, it is very gentle on the tape. After the cassette is inserted into the drive, the tape is pulled out and wrapped around the read/write head. While the head rotates as much as 30 meters per second, the tape travels as little as 1 inch per second (ips), compared to linear technologies where the tape travels at more than 100 ips.

Helical scan was invented by Ampex in 1956. It was the only method that provided fast-enough transfer rate and sufficient storage capacity to record video on tape so that TV programs could be recorded. Using two-inch tape and running at 15 ips, the going rate for tape recorders of the time, the rotating head created an effective rate of 1500 ips. The helical scan method is used in many different tape technologies, including VHS videotape, DV/MiniDV (camcorders), 4mm DAT, Exabyte's 8mm and Mammoth lines, Sony's AIT and StorageTek's Redwood.


Helical Scan
The helical scan method uses a rotating head and diagonal tracks, which allows a slow-traveling tape to provide a very fast transfer rate. The tape is pulled out of the cartridge and wrapped around the read/write head.


Helical Scan
The helical scan method uses a rotating head and diagonal tracks, which allows a slow-traveling tape to provide a very fast transfer rate. The tape is pulled out of the cartridge and wrapped around the read/write head.







Helical Scan Formats
As you can see from this illustration, there are numerous helical scan formats used for digital storage. The predecessors to VHS tape (top) were the reason for helical scan in the first place. Although mostly used for analog recording, there have been digital applications of VHS tape as well.


Helical Scan Formats
As you can see from this illustration, there are numerous helical scan formats used for digital storage. The predecessors to VHS tape (top) were the reason for helical scan in the first place. Although mostly used for analog recording, there have been digital applications of VHS tape as well.







The Real Thing
Notice the slant on this helical scan head from a VHS video recorder. This precise angle of the head is used to record and play back all helical scan formats.

helical scan

helical scanclick for a larger image
In radar scanning, varying the azimuth and elevation of the antenna continuously to generate a spiral pattern of the beam. This scan pattern is used in fire-control and GCI (ground-controlled interception) radars. Also called spiral scanning.
References in periodicals archive ?
Both the linear and helical scan tape drives and the disk drive keep an accurate record of the location of data on the recorded media.
The physical properties of MP media were quite attractive to meet the demands of DDS helical scan recording.
Normally, helical scan drives keep very close control of the tape in the tape path.
Helical Scan Recording Technology - Helical scan recording technologies, based on a very stable rotating drum/head platform, permit accurate and reliable data recording at very high track densities.
Evans continued, "Adding LTO media compliments this strategy to provide leading linear tape and helical scan technologies for a variety of users and applications.
Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan
Other Emmy awards include: 1957 for the development of the videotape recorder; 1967 for the development of the color VTR-2000; 1978 for Automatic Scan Tracking for tape slow motion; 1978 for the Type-C format videotape recorder; 1981 for Electronic Still Store; 1983 for Digital Special Effects; 1984 for the first helical scan portable videotape recorder; 1986 for the Advanced Digital Video Processor; 1989 for digital video recording technology development; and 1990 for automated commercial spot players.
Helical Scan Products: Track is recorded diagonally in "stripes" across face of longitudinal tape.
Exabyte Corporation (Nasdaq: EXBT), a performance leader in network backup, today announced that Data Storage magazine has released test results proving that the Mammoth-2 (M2(TM)) tape drive has four times the performance of other helical scan tape drives on the market.
Digital Data Storage (DDS) is a helical scan format where data is written diagonally across the width of the tape.