Page 270 - DCAP103_Principle of operating system

Unit 7: Secondary Storage Structure

12. What would be the effects on cost and performance if tape storage had the same areal Notes
density as disk storage?
13. If magnetic hard disks eventually have the same cost per gigabyte as do tapes, will tapes
become obsolete, or will they still be needed? Explain your answer.
14. Imagine that a holographic storage drive has been invented. Suppose that a holographic
drive costs $10,000 and has an average access time of 40 milliseconds. Suppose that it uses
a $100 cartridge the size of a CD. This cartridge holds 40,000 images, and each image is
a square black and white picture with resolution 6,000 x 6,000 pixels (each pixel stores 1
bit). Suppose that the drive can read or write one picture in 1 millisecond.

15. Answer the following questions:
(a) What would be some good uses for this device?
(b) How would this device affect the 1/0 performance of a computing system?

(c) Which other kinds of storage devices, if any, would become obsolete as a result of this
device being invented?

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16. Suppose that we agree that 1 KB is 1,024 bytes, 1 MB is 1,024 bytes, and 1 GB is 1,024 bytes.
This progression continues through terabytes, petabytes, and exabytes (1,024 ). Several
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newly proposed scientific projects plan to be able to record and store a few exabytes of
data during the next decade. To answer the following questions, you will need to make
a few reasonable assumptions; state the assumptions that you make.
(a) How many disk drives would be required to hold 4 exabytes of data?

(b) How many magnetic tapes would be required to hold 4 exabytes of data?
(c) How many optical tapes would be required to hold 4 exabytes of data?

(d) How many holographic storage cartridges would be required to hold 4 exabytes of
data?

(e) How many cubic feet of storage space would each option require?
17. Consider a RAID Level 5 organization comprising five disks, with the parity for sets of
four blocks on four disks stored on the fifth disk. How many blocks are accessed in order
to perform the following?
(a) A write of one block of data.
(b) A write of seven continuous blocks of data.

Answers to Self Assessment

1. (c) 2. (a) 3. (b) 4. (c) 5. (b)
6. (b) 7. (c) 8. (a) 9. disk

10. pseudo-swap 11. round-robin

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