Page 247 -

214 CHAPTER 6 / EXTERNAL MEMORY

6.6 KEY TERMS, REVIEW QUESTIONS,AND PROBLEMS

Key Terms

access time DVD-RW pit
Blu-ray fixed-head disk platter
CD floppy disk RAID
CD-ROM gap removable disk
CD-R head rotational delay
CD-RW land sector
constant angular velocity magnetic disk seek time
(CAV) magnetic tape serpentine recording
constant linear velocity (CLV) magnetoresistive striped data
cylinder movable-head disk substrate
DVD multiple zoned recording track
DVD-ROM nonremovable disk transfer time
DVD-R optical memory

Review Questions
6.1 What are the advantages of using a glass substrate for a magnetic disk?
6.2 How are data written onto a magnetic disk?
6.3 How are data read from a magnetic disk?
6.4 Explain the difference between a simple CAV system and a multiple zoned recording
system.
6.5 Define the terms track, cylinder, and sector.
6.6 What is the typical disk sector size?
6.7 Define the terms seek time, rotational delay, access time, and transfer time.
6.8 What common characteristics are shared by all RAID levels?
6.9 Briefly define the seven RAID levels.
6.10 Explain the term striped data.
6.11 How is redundancy achieved in a RAID system?
6.12 In the context of RAID, what is the distinction between parallel access and indepen-
dent access?
6.13 What is the difference between CAV and CLV?
6.14 What differences between a CD and a DVD account for the larger capacity of the latter?
6.15 Explain serpentine recording.
Problems

6.1 Consider a disk with N tracks numbered from 0 to (N 1) and assume that re-
quested sectors are distributed randomly and evenly over the disk.We want to calcu-
late the average number of tracks traversed by a seek.
a. First, calculate the probability of a seek of length j when the head is currently po-
sitioned over track t. Hint: This is a matter of determining the total number of
combinations, recognizing that all track positions for the destination of the seek
are equally likely.