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Measurement Definition
Measurement Parameter Definition
Figure 5-25
Characteristic curve of the 747 test
Figure 5-25 shows how much off-track (OTC) can be afforded between the data track and
the read head for a fixed error rate level for a specific distance to an adjacent track. The 747
test is an excellent test to determine the optimum number of tracks per inch. At the peak of
the 747 hump you are at the closest distance from the track center with the widest OTC, i.e.
the optimum point.
The measurement procedure of the 747 test is as follows:
1. Write an old data with a fix position from the data track.
2. Overwrite the old data track with a new data track.
3. Write an adjacent track with a particular distance offset from the data track.
4. Measure the off-track capability (OTC).
5. Decrease the adjacent track offset, then iterate steps 4 and 5.
270
Chapter 5
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