Question

In a computer system, four files of size 11050 bytes. 4990 bytes, 5170 bytes and 12640 bytes need to be stored. For storing these files on disk, we can use either 100 byte disk blocks or 200 byte disk blocks (but can't mix block sizes). For each block used to store a file, 4 bytes of bookkeepiing information also needs to be stored on the disk. Thus, the total space used to store a file is the sum of the space taken to store the file and the space taken to store the book keeping information for the blocks allocated for storing the file. A disk block can store either bookkeeping information for a file or data from a file, but not both.

What is the total space required for storing the files using 100 byte disk blocks and 200 byte disk blocks respectively?

• A. 35400 and 35600 bytes
• B. 35400 and 35800 bytes
• C. 35800 and 35400 bytes
• D. 35600 and 35400 bytes

Answer 1

The correct option is D 35600 and 35400 bytes

Using 100 bytes disk block:
100 B

File size	100 B block	Bytes needed for Book keeping	Block for Information
11050 4990 5170 12640	111 50 52 127	111 $\times$ 4 = 44 50$\times$4=200 52$\times$4=208 127$\times$4=508	5 2 3 6
Total	340		16

Space $=(340+16)\times 100=35600$

Using 200 bytes disk block:
200 B

File size	100 B block	Bytes needed for Book keeping	Block for Information
11050 4990 5170 12640	56 25 26 64	56 $\times$ 4 = 244 25$\times$4=100 26$\times$4=104 64$\times$4=256	2 1 1 2
Total	171		6

Space $=(171+6)\times 200=35400$