Section 17.3
Review Questions
Data encoding techniques for disk drives
  1. Sometimes there are little holes in disk drives that enable the electronics to determine where sectors start. If this is so, we say the disks are...
answer...
hard-sectored
  1. Are all 1's and 0's on the surface of a disk surface really data?
answer...
No, some sequences of 1s and 0s are special bit patterns that have meanings such as "no data here."
  1. How would the data pattern 1101 be stored using Manchester encoding?
answer...
01011001

or 01 01 10 01
   1  1  0  1
  1. What do we call it when the electronics lose sight of the boundaries between bits and begin to misinterpret the patterns?
answer...
drift
  1. How would a long sequence of the same bit values cause problems? For example, 000000000.... or 1111111111....
answer...
Drift might occur if the clocks of the two components were not precisely in synch.
  1. Why is Manchester encoding good in this kind of situation?
answer...
because it forces a series of regular transitions between the two voltage levels that represent 1 and 0, and the electronics can sense these transitions and reset their clocks to stay in synch.