How do you ordering the optimal storage on tapes?

Answer 1

OPTIMAL STORAGE ON TAPES

We want to store files of lengths (in MB) {12,34,56,73,24,11,34,56,78,91,34,91,45} on

three tapes. How should we store them on the three tapes so that the mean retrieval

time is minimized?

SOLUTION: STORE FILES BY NON-DECREASING LENGTH

First sort the files in increasing order of length. For this we can use heap sort, merge sort

or quick-sort algorithms.

11 12 24 34 34 34 45 56 56 73 78 91 91

Now distribute the files:

First element 11

Tape 11

1

Tape

2

Tape

3

Second element 12

Tape 11

1

Tape 12

2

Tape

3

Third element 24

Tape 11

1

Tape 12

2

Tape 24

3

Fourth element 34

Tape 11 34

1

Tape 12

2

Tape 24

3

Fifth element 34

Tape 11 34

1

Tape 12 34

2

Tape 24

3

Sixth element 34

Tape 11 34

1

Tape 12 34

2

Tape 24 34

3

Seventh element 45

Tape 11 34 45

1

Tape 12 34

2

Tape 24 34

3

Eigth element 56

Tape 11 34 45

1

Tape 12 34 56

2

Tape 24 34

3

Ninth element 56

Tape 11 34 45

1

Tape 12 34 56

2

Tape 24 34 56

3

Tenth element 73

Tape 11 34 45 73

1

Tape 12 34 56

2

Tape 24 34 56

3

Eleventh element 78

Tape 11 34 45 73

1

Tape 12 34 56 78

2

Tape 24 34 56

3

Twelth element 91

Tape 11 34 45 73

1

Tape 12 34 56 78

2

Tape 24 34 56

3

Thirteenth element 91

Tape 11 34 45 73

1

Tape 12 34 56 78

2

Tape 24 34 56

3

Answer 2

There are two methods of storing data on tapes:

1. magnetic, this is the most common method used today. the tape is coated with magnetizable particles and an electromagnetic head is used to both write and read data on this coating.
2. punched holes, metal punches/dies punch holes in the tape corresponding to the data, readout can be performed with mechanical feelers, metal electrical brushes, or photo sensors.