Skew
From Wikipedia, the free encyclopedia
The term skew, generally referring to some difference from an expected or optimal value, is common in both telecommunications and mathematics. Skew has also acquired a new meaning for computer disk drives.
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[edit] Telecommunication
- In parallel transmission, the difference in arrival time of bits transmitted at the same time.
- For data recorded on multichannel magnetic tape, the difference between reading times of bits recorded in a single transverse line.
Note: Skew is usually interpreted to mean the difference in reading times between bits recorded on the tracks at the extremities, or edges, of the tape.
- In facsimile systems, the angular deviation of the received frame from rectangularity caused by asynchronism between the scanner and the recorder.
Note: Skew is expressed numerically as the tangent of the deviation angle.
- In facsimile, the angle between the scanning line, or recording line, and the perpendicular to the paper path.
- Example of +1 degree (counter-clockwise) skew in a facsimile image. The red line is perfectly horizontal.
Source: from Federal Standard 1037C and from MIL-STD-188
[edit] Computers
- In reference to computer disk drives, track-to-track skew is the angle between the start of the data on a given track and the start of the data on the next. This is important, as when reading the data in sequence from one track to the next, time must be allowed for the read/write head to move to the next track, during which the disk continues to rotate. Insufficient skew can force the drive to wait almost an entire revolution for the data to pass under the head again, resulting in extra revolutions per track to read the data. Excessive skew can also lower the sustained data transfer rate.
[edit] Computer graphics
Skew is a common term for the shear transformation.
[edit] Mathematics
- In statistics, skew can refer to the skewness of a distribution.
- In linear algebra, a skew-symmetric matrix is a matrix which is the negative of its own transpose.
- In geometry, skew lines are lines which do not intersect yet are not parallel.
[edit] Optics
In optics, a skew ray is an optical path through a rotationally symmetric optical system that is not in a plane of symmetry.
