OS: Case Study 3

In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems. Name at least two of these problems. Can we ensure the same degree of security in a time-share machine as we have in a dedicated machine? Explain your answer

A multiprogramming is a method of simultaneous execution on a digital computer of several programs related to different problems. Multiprogramming system is that system in which multiple programs run at same time or simultaneously for example windows xp.in this system does not provide user interaction with the computer system. But time sharing systems that provide user interaction with system and user thinks that system is with him all the time.

Some problems are: Data confidentiality having secret or confidential data remains so defining and enforcing who can see what – authorization authentication. Stealing or copying one's programs or data; using system resources (CPU, memory, disk space, peripherals) without proper accounting. Unauthorized user or program cannot modify data without owner’s permission. Writing over another program's (belonging to another user or to the OS) area in memory. Using system resources (CPU, disk space) without proper accounting; Causing the printer to mix output by sending data while some other user's file is printing.


The more complex the scheme, the more difficult it is to feel confident of its correct implementation. Security depends on the key strength number of keys type of algorithm key distribution system reliability of persons and other such parameters in cryptology hence time sharing or dedicated machines.

The time-sharing mode gives every user the impression that the computer is working for him alone. Each user is supplied with a data input-output device (of the display type) or other equipment that ensures interaction with the computer. This includes equipment that uses telephone lines. Each user solves his problem periodically during the machine time allocated to him, studies the results, and prepares the next assignment for the computer. The user ordinarily uses a general library of programs, but he may also have a private archive. If the general library is used, a supervisory program plans and executes forced interruptions of programs depending on user priority, machine time allocated to him, and the nature of the problem being solved. The time-sharing mode permits the user to carry on an effective dialogue with the machine, which is most convenient in control systems for production processes, automatic control systems for enterprises and sectors of the national economy, reference and information services, and large computer centers. When it is not serving users, the computer may do batch processing.
Multiprogramming is provided by hardware and software. The hardware includes memory protection and the organization of interruptions. The software includes supervisory programs and problem-oriented programming languages that take into account the characteristics of multiprogramming.