Pos/355 Chapt 10 Questions

10.1 Some systems automatically delete all user files when a user logs off or a job terminates, unless the user explicitly requests that they be kept; other systems keep all files unless the user explicitly deletes them. Discuss the relative merits of each approach.

Deleting all files not specifically saved by the user has the advantage of minimizing the file space needed for each user by not saving unwanted or unnecessary files. Saving all files unless specifically deleted is more secure for the user in that it is not possible to lose files inadvertently by forgetting to save them.

10.2 Why do some systems keep track of the type of a file, while others leave it to the user and others simply do not implement multiple file types? Which system is “better?”

Some systems allow different file operations based on the type of the file (for instance, an ASCII file can be read as a stream while a database file can be read via an index to a block). Other systems leave such interpretation of a file's data to the process and provide no help in accessing the data. The method that is better depends on the needs of the processes on the system, and the demands the users place on the operating system. If a system runs mostly data based applications, it may be more efficient for the operating system to implement a database-type file and provide operations, rather than making each program implement the same thing (possibly in different ways). For general-purpose systems it may be better to only implement basic file types to keep the operating system size smaller and allow maximum freedom to the processes on the system.

10.3 Similarly, some systems support many types of structures for a file’s data, while others simply support a stream of bytes. What are the advantages and disadvantages of each approach?

An advantage of having the system support different file structures is that the support comes from the system; individual applications are not required to provide the...