Case Study 4:

Using the process state diagram, explain why there is no transition: From the READY to WAITING and from the WAITING to RUNNING.

A computer program that is subsequently executed is called process.  Process management is an operating system's way of dealing with running multiple processes on a single CPU. In a multitasking computer system, processes may occupy a variety of states.  On the diagram above, we can see that there is no transition from the ready to waiting same with waiting to running. In the ready state to waiting state, there is no transition between them because you can only send the job in the waiting state if it came from the running state. Also, it will proceed to the waiting state if there are some interrupts and if it needs input/output request. In the waiting state to running state, there is also no transition because the process scheduler selects processes from the ready state for the CPU. Also, all jobs in the waiting list was arranged and prepared to proceed in the ready state.  In addition, only the ready jobs or only the jobs in the ready state will proceed to the running state to be run and to bypass the ready state would make process management impossible.

To further understand the process let us assign job (a) to be processed.

First job (a) will go to the hold state then it will proceed to ready state. If the job will fail because of some device failure it will go back to the hold state, if not, it will proceed to ready state which is controlled by the job scheduler. From the ready state, job (a) will go on to the running state. If there are no interrupts and there are no input/output request faults it will automatically proceed to the finished state. But, if it will encounter interrupts it will go back to the ready state and if it fails to have the input/output request it will proceed to the waiting state. 




Resources:
http://iamleianjui.blogspot.com/2011/02/case-study-6-using-process-state.html

CS323: Case Study 3

CS323: Case Study 3

Load the following jobs into memory using fixed partition following a certain memory allocation method (a. best-fit, b. first-fit, c. worst-fit).

Memory Block	Size
Block 1	50K
Block 2	200K
Block 3	70K
Block 4	115K
Block 5	15K

a. Job1 (100k) f. Job6 (6k)

turnaround: 3 turnaround: 1

b. Job2 (10k) g. Job7 (25k)

turnaround: 1 turnaround: 1

c. Job3 (35k) h. Job8 (55k)

turnaround: 2 turnaround: 2

d. Job4 (15k) i. Job9 (88k)

turnaround: 1 turnaround: 3

e. Job5 (23k) j. Job10 (100k)

turnaround: 2 turnaround: 3

*turnaround – how long it will stay in the memory.

Instructions:

View in large scale. 

 

View in large scale.

 

View in large scale.

Resources: http://anev11.blogspot.com/2011/01/os-case-study-5.html

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