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Measurement Definition
Measurement Parameter Definition
Analysis of the 747 Test
The purpose of the 747 test is to determine the off-track capability of the magnetic
recording system. The off-track capability helps us to know how close tracks of
information can be written on a magnetic media without picking up the interference signal
of its adjacent track. The off-track capability is measured between the center of the data
track and the center of the head gap. The 747 test is also used to determine the maximum
track pitch in order optimize the number of tracks per inch (TPI) of a magnetic recording
system.
When a head is shifted off the track center, it picks up some part of the readback-signal
from the data track and some noise signal from the media. When an adjacent track is
written close to the data track, it limits the off-track capability (OTC) of the recording
system, as it picks up interference signal from the adjacent track.
Figure 5-21
Old Data Pattern are written first
In performing the 747 test, we must first write the old track or old information with a fixed
distance from the data track.
Figure 5-22
The old data pattern is overwritten by the data track
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Chapter 5
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