Assignment 5 

1. Some operating systems provide a system call RENAME to give a file a new name.  Is there any difference at all between using this call to rename a file, and just copying the file to a new file with the new name, followed by deleting the old one?
2. Contiguous allocation of files leads to disk fragmentation.  Is this internal or external fragmentation?
3. It has been suggested that the first part of each UNIX file be kept in the same disk block as its inode.  What good would this do?
4. Would compacting disk storage periodically be of any conceivable value? Explain.
5. When a file is removed, its blocks are generally put back on the free list, but they are not erased.  Do you think it would be a good idea to have the operating system erase each block before deleting it?  Consider both security and performance factors in your answer, and explain the effect of each.
6. Two computer science students, Carolyn and Elinor, are having a discussion about i-nodes.  Carolyn maintains that memories have gotten so large and so cheap that when a file is opened, it is simpler and faster just to fetch a new copy of the inode into the inode table, rather than search the entire table to see if it is already there.  Elinor disagrees.  Who is right?
7. If a disk controller writes the bytes it receives from the disk to memory as fast as it receives them, with no internal buffering, is interleaving conceivably useful? Discuss.
8. Disk reauests come in to the disk driver for cylinders 10, 22, 20, 2, 40, 6, and 38, in that order.  A seek takes 6 msec per cylinder moved.  Assuming for all cases the arm is initially at cylinder 20, how much seek time is needed for: a) FCFS b) Closest cylinder first or SSTF c) Elevator algorithm (initially moving upwards). 
9. Why are RS232 terminals interrupt driven, but memory mapped terminals are not?
10. RAID 2 gives a lower I/O request rate than RAID 0 and RAID 1.  Explain why.


11. A password may become known to other users in a variety of ways. Is there a simple method for detecting that such an event has occurred? Explain your answer.
12. The list of all passwords is kept within the operating system. Thus, if a user manages to read this list, password protection is no longer provided. Suggest a scheme that will avoid this problem. (Hint: Use different internal and external representations.)
13. Discuss ways by which managers of systems connected to the Internet could have limited or eliminated the damage done by the worm. What are the drawbacks of making such changes to the way in which the system operates?
14. What are the main differences between capability lists and access lists?
15. If all the access rights to an object are deleted, the object can no longer be accessed. At this point, the object should also be deleted, and the space it occupies should be returned to the system. Suggest an efficient implementation of this scheme.