helical scan


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helical scan

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

Invented by Ampex in 1956, helical scan was the only method that was fast enough to record video in real time. 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 was 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 used a rotating head and diagonal tracks, which allowed a slow-traveling tape to provide a very fast transfer rate. The tape was pulled out of the cartridge and wrapped around the read/write head.


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







Helical Scan Formats
There were numerous helical scan formats used for digital storage.


Helical Scan Formats
There were numerous helical scan formats used for digital storage.







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

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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.
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References in periodicals archive ?
Based on the D-2 tape format (19-mm helical scan), the system is an outgrowth of Ampex's VPR-300 Digital Video Broadcast Recorder (Figure 3).
Information is recorded on these tapes in a variety of fashions, such as linear tracks, multiple linear tracks, helical scans and rotary transverse scans.
In order to overcome problems of modulation noise and signal dropout at the very high head-to-tape speeds of helical scan recording, it is essential that the tape's magnetic base film be exceptionally smooth.
SFF Half-Inch Cartridge/ Other Data Cartridge 22.14% 8mm Helical Scan 4.78% 4mm Helical Scan 50.95% 1/4-Inch Data Cartridge 4.25% Minicartridge 17.89% Figure 1- DDS drives (4mm helical scan) have maintained their dominant market share (Source: Gartner Dataquest) Note: Table made from pie chart.
As far as capacity futures are concerned DAT/DDS, 8mm, AIT, and VXA helical scan products have less available total tape area than the linear technology products Travan, SC50, SLR, LTO, and DLT tape formats.
One of them is Sony's AIT-1, the helical scan tape product introduced originally in 1996.
The MSS implemented virtualization by making the physical storage, actually robotically retrieved helical scan tapes, appear as rotating magnetic disk drives to the operating system.
As another high-capacity format seeking to take market share from the industry leader DLT, Exabyte's Mammoth 2 is currently the highest-capacity helical scan format available with a native capacity of 60GB and a native transfer rate of 12MB/sec.
Multiple choices in both linear and helical scan formats offer users more freedom to choose the tape option that best meets their requirements, from small offices to departmental and workgroup environments to multi-terabyte enterprise applications.
Intravenously, 125 mL of 68% iodinated contrast material was administered as a sustained bolus at 4 mL/sec, after which dynamic helical scans (LightSpeed, GE Healthcare, Chalfont St.