Assignment

Question One

"chmod" is a well known command line utility, that is used for manually managing the access and permissions to files and directories on MacOS, Linux and other Unix like operating systems. Explain how the file permissions are changed after executing this command:
$ chmod 624 SEUfile.txt

Question Two

Consider a file system on a disk that has both logical and physical block sizes of 512 bytes. Assume that the information about each file is already in memory. For each of the three allocation strategies (contiguous, linked, and indexed), answer these questions:

a. How is the logical-to-physical address mapping accomplished in this system? (For the indexed allocation, assume that a file is always less than 512 blocks long.)

b. If we are currently at logical block 10 (the last block accessed was block 10) and want to access logical block 4, how many physical blocks must be read from the disk?

Question Three

a) Explain the ways of disk attachments used by computers to access memory disk.

b) Explain C-SCAN disk scheduling algorithm with example?

Question Four

Suppose that a disk drive has 5,000 cylinders, numbered 0 to 4,999. Thedrive is currently serving a request at cylinder 2,150, and the previous request was at cylinder 1,805. The queue of pending requests, in FIFO order is as below:

2069, 1212, 2296, 2800, 544, 1618, 356, 1523, 4965, 3681

Starting from the current head position, what is the total distance (incylinders) that the disk arm moves to satisfy all the pending requestsfor each of the following disk-scheduling algorithms?

a) LOOK
b) C-LOOK.