Assignment 7

1. Briefly explain the differences between seek time and search time. In your opinion, why do some people confuse the two?

2. Given the following characteristics for a magnetic tape using linear recording as described in this chapter:

Density = 1600 bpi

Speed = 1500 inches/second

Size = 2400 feet

Start/stop time = 4 ms

Number of records to be stored = 200,000 records

Size of each record = 160 bytes

Block size = 10 logical records

IBG = 0.5 inch

Find the following:

a. Number of blocks needed

b. Size of the block in bytes

c. Time required to read one block

d. Time required to write all of the blocks

e. Amount of tape used for data only, in inches

f. Total amount of tape used (data + IBGs), in inches

3. Given that it takes 1.75 ms to travel from one track to the next of a hard drive; that the arm is originally positioned at Track 15 moving toward the low- numbered tracks; and that you are using the LOOK, C-SCAN, and C-LOOK scheduling policy:

Compute the total seek time to satisfy the following requests4, 40, 35, 11, 14, and 7. Assume all requests are initially present in the wait queue. (Ignore rotational time and transfer time; just consider seek time.)

4. Consider a virtual cylinder identical to the one shown in Figure 7.12 with the following characteristics: seek time is 4 ms/track, search time is 1.7 ms/sector, and data transfer time is 0.9 ms. Calculate the resulting seek time, earch time, data transfer time, and total time for the following Request List, assuming that the read/write head begins at Track 0, Sector 0. Finally, calculate the total time required to meet all of these requests.

Track	Sector
1	0
1	4
1	0
3	1
2	4
3	0

5. Using an identical environment to the previous question, calculate the resulting seek time, search time, data transfer time, and total time for the following:

Request List, assuming that the read/write head begins at Track 3, Sector 0.

Calculate the total time required.

Track	Sector
2	5
1	2
1	0
2	3
2	4
1	0

6. We received 1110110 1110110. A one bit error has occurred during the reception of the code word.

A. Find out the error bit?

B. What is the original data?

7. Describe how implementation of a RAID Level 1 system would be beneficial to a university payroll system. In your own words, describe the advantages and the disadvantages of such a system, if any, in that environment, and if appropriate, suggest an alternative RAID system and explain your reasoning.