Lesson plan
Write precompensation
Write precompensation (abbreviated WPcom in the literature) is a technical aspect of the design of hard disks, floppy disks and other digital magnetic recording devices. It is the modification of the analog write signal, shifting transitions somewhat in time, in such a way as to ensure that the signal that will later be read back will be as close as possible to the unmodified write signal. It is required because of the non-linear properties of magnetic recording surfaces. A higher amount of precompensation is needed to write data in sectors that are closer to the center of the disk. In constant angular velocity (CAV) recording, in which the disk spins at a constant speed no matter where the data is written, the sectors closest to the spindle are packed tighter than the outer sectors and so require a slightly different timing to write the data in the most reliable way. CAV recording is used by most floppy disk systems and by older hard disk systems; the term CAV is not applicable to non-circular media, such as magnetic tapes, on which precompensation is usually constant throughout the tape.
Article summary
Write precompensation (abbreviated WPcom in the literature) is a technical aspect of the design of hard disks, floppy disks and other digital magnetic recording devices. It is the modification of the analog write signal, shifting transitions somewhat in time, in such a way as to ensure that the signal that will later be read back will be as close as possible to the unmodified write signal. It is required because of the non-linear properties of magnetic recording surfaces. A higher amount of precompensation is needed to write data in sectors that are closer to the center of the disk. In constant angular velocity (CAV) recording, in which the disk spins at a constant speed no matter where the data is written, the sectors closest to the spindle are packed tighter than the outer sectors and so require a slightly different timing to write the data in the most reliable way. CAV recording is used by most floppy disk systems and by older hard disk systems; the term CAV is not applicable to non-circular media, such as magnetic tapes, on which precompensation is usually constant throughout the tape.
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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