UGC NET CSE | September 2013 | Part 2 | Question: 47

Question

Assume that an implementation of Unix operating system uses i-nodes to keep track of data blocks allocated to a file. It supports 12 direct block addresses, one in direct block address and one double indirect block address. The file system has 256 bytes block size and 2 bytes for disk block address. The maximum possible size of a file in this system is

• A. 16 MB
• B. 16 KB
• C. 70 KB
• D. 71 KB

Comments

I think maximum file size is get when we consider double indirect block address.

• Each indirect block stores 256/2 =128 pointers.
• double indirect block can point 128 x 128 blocks
• Maximum file size is 128x128x256 = 4194304 B= 4096 KB =4MB

Correct me please if I went wrong somewhere

Answer 1

direct block addressing will point to 12 disk blocks=12*256B

Singly Indirect block addressing will point to 1 disk block which has 256/2 disc block addresses

                                                                            =128*256B

Doubly indirect block addressing has (256/2)*(256/2) disk block addresses

                                                                           =128*128*256B

Total File Size=(12+128+128*128)*256B

                      =4131KB

 

Or Alternatively you can do direct by formula

Max File size in File System=[#of Direct DBA +(DB Size/DBA)+(DB Size/DBA)^2+(DB Size/DBA)^3+........]*DB Size

 

Max File Size possible in file System=[ 12+ 256/2+ (256/2)^2]*256B

                                                        =4131KB

                                                         or 4MB(apx)

No option is true.

Comments

Yes even i didnt get any option true . So i thought i was wrong thanks :)

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What are the parameters of the formulae? Please post it.

Answer 2

File size possible is 12* 256 + (256/2)*(256) +  (256/2)(256/6)*256  .

Maximum file size is (256/2)(256/2)*256  .

I am not sure . Let other verifythis !

Answer 3

I think memory access heirarchy is :

Double indirect addressing block -> indirect addressing block -> direct addressing block -> file block

 

So Max file size would be 128*128*128*256B = 512 MB