CS323: Case Study 2

Based on what I researched I got a lot idea that in a multiprogramming and time-sharing environment, several users share the system simultaneously and this situation can result in various security problems like;

Two of the most possible problems of this environment are:

1. One user can copy another user's program / memory space. This could be very harmful if, for example, an administrator was running a decryption procedure, and another user stole the decryption program and/or key. And this will result to stealing a user's file.

2. The second problem is, Resource usage may not be completely controlled, and could cause deadlock for certain users. For example, if user A had resource 1 and was waiting for resource 2, and user B had resource 2 and was waiting for resource 1, deadlock would occur and neither user would be able to make progress in their program, no matter how many time slots they were allocated.

And for the question that, can we ensure the same degree of security in a time-share machine as we have in a dedicated machine?

My answer would be, probably not, because based on my researched, 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. 

 For you to know what is MULTIPROGRAMMING and TIME-SHARING here is their meaning:

Multiprogramming: When multitasking is just talking about executing multiple programs concurrently then the term multitasking term is referred as multiprogramming.

Time sharing: This is somewhat different in some sense to both multitasking and multiprogramming.In time sharing several systems(called as dumbed servers having only computer peripherals -no CPUs they have) are attached to a single dedicated server having own CPU. Dumbed servers share the CPU of dedicated server as they don't have their own CPUs. Every action or command in Time sharing operating systems is so short that very short span of CPU time is assigned for each user and thus the users at dumbed systems have an impression that they have their own CPU though the fact is they share the CPU of dedicated server. Such short periods of time is called as time-slots or time-slices.or time-quantum.

Resources: http://web.engr.oregonstate.edu/~pancake/cs411/hw1sol.s99.html