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Rare Earths
Metallic elements of the lanthanide series
(atomic numbers 57 through 71) in the chemical periodic
table, such as Praeseodymium, Neodimium, Samarium,
Gadolinium and Dysprosium, which are used to form the
thin magnetic layer in rewritable optical disks.
Read/Write Head
A head which may be shifted horizontally to the
disk surface and which consists of at least one
electro-magnet. The head may magnetise the disk surface
(write on it), read it and erase it; erasing being a
write process with a regular pattern.
Recording Density
The number of all magnetised points on the
magnetic data carrier. Measured in bits per inch (bpi)
and tracks per inch (tpi).
Reed-Solomon Code
An error detection code or an error correcting
code or a combination of both which is particularly
suited to the correction of burst errors or errors that
are strongly correlated.
RLL
Run Length Limited.
Recording method for hard disk drives with a high
recording density.
Rotary Voice Coil Actuator
In principle, the rotary voice coil actuator
consists of a movable wire coil in a stationary magnetic
field (similar to the principle of a loudspeaker). When
there is current flowing through the coil, the resulting
magnetic field interacting with the permanent magnet
causes a movement which again acts on the positioning
arm. This movement may be varied infinitely (linear) with
the current strength.
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