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?
First and foremost, let me define the meaning of multiprogramming as well as time-sharing. Multiprogramming refers to the allocation of a computer system and its resources to more than one concurrent application, job or user (“program” in this nomenclature). Initially, this technology was sought in order to optimize use of a computer system, since time and processing resources were often wasted when a single job waited for human interaction or other data input/output operations. Its capability was developed as a future of operating system the late 1950s and came into common use in mainframe computing in the mid-to late 1960s. This followed the development of hardware systems that processed the requisite circuit logic and instruction sets to facilitate the transfer of control between the operating system and one more independent applications, users or job streams. The use of multiprogramming was enhanced by the arrival of virtual memory and virtual machine technology, which enabled individual programs to make use of memory and operating system resources as if other concurrently running programs were, for all practical purpose, non-existent and invisible to them. Multiprogramming should be differentiated from multi-tasking since not all multiprogramming entails—or has the capability for—“true” multi-tasking. This is the case even thought the use of multi-tasking generally implies the use of some multiprogramming methods. In this context, the root word “program” does not necessarily refer to a compiled application, rather, any set of commands submitted for execution by a user or operator. Such could include a script or job control stream and any included calls to macro-instructions, systems utilities or application program modules. An entire, interactive, logged in user session can be thought for as a “program” in this sense.
On the other hand, time-sharing means the sharing of computer resource among many users by means of multiprogramming and multi-tasking. By allowing a large number of users to interact concurrently with a single computer, time-sharing dramatically lowered the cost of providing computing capability, made it possible for individuals and organizations to use a computer without owning one, and promoted the interactive use of computers and the development of new interactive applications. In time-sharing systems, the running task is required to relinquish the CPU, either, voluntarily or by an external event such as a hardware interrupt. Time sharing systems are designed to allow several programs to execute apparently simultaneously. The expression ‘time sharing’ was usually used to designate computers shared by interactive users at terminals, such as IBM’s TSO, and VM/CMS.
After I have define what multiprogramming and time-sharing is, now my turn to answer what are the possible security problems that may occur during this situation. A program generally comprises numerous tasks, a task being a relatively small group of processor instruction of a continuous-running application program. A task frequently ends with some request requiring the moving of data, a convenient opportunity to allow another program to have system resources, particularly CPU time.
My first answer will be, there will have an increasing possibility of hacking a certain files of the certain user as well as being prone and may lead to uncertain doing such as having a copyright to a certain files that supposedly and restrictedly to be copied or maybe opening of uncertain and private documents of the user. So it is not really safe to have this sharing the system simultaneously aside from this, it will lower the execution of the programs and different jobs. Another one is there will be a big possibility that the files of the user will be interchange because of the time-sharing method or resource usage may not be completely controlled. There are huge chances of losing your files or maybe there comes the time that your files have unknown documents and sometimes as what I have observed it is the way where viruses attack. They will disguise as a new file but surprisingly it is already a virus. To a great extent, the ability of a system to share its resources equitably—or according to a certain priorities—is dependent upon the design of the programs being handled and how frequently they may be interrupted.
Lastly, my answer for the question, “Can we ensure the same degree of security in a time-share machine as we have in a dedicated machine?”, my response will be probably not, since any protection scheme devised by a human can also be broken—and the more complex the scheme is, the more difficult it is to be confident of its correct implementation. Moreover, when multiple programs are present in memory, an ill-behaved program may (inadvertently or deliberately) overwrite memory belonging to another program, or even to the operating system itself. So we cannot really ensure the same degree of security in a time-sharing machine.
