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Operating Systems - Basic premise

1. In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems.
a. What are two such problems?
b. Can we ensure the same degree of security in a time-shared machine as in a dedicated machine? Explain your answer.

2. What network configuration would best suit the following environments? Explain your answers.
a. A dormitory floor
b. A university campus
c. A state
d. A nation

3. Describe the five major activities of an operating system in regard to file management?

4. What is the main advantage for an operating-system designer of using a virtual-machine architecture? What is the main advantage for a user?

5. Describe the differences among short-term, medium-term, and long term scheduling.

6. What are the benefits and detriments of each of the following? Consider both the systems and the programmers' levels.
a. Synchronous and asynchronous communication
b. Automatic and explicit buffering
c. Send by copy and send by reference
d. Fixed-sized and variable-sized messages

7. Provide two programming examples in which multi-threading does not provide better performance than a single-threaded solution.

8. Can a multi-threaded solution using multiple user-level threads achieve better performance on a multiprocessor system than on a single-processor system? Explain.

9. Discuss how the following pairs of scheduling criteria conflict in certain settings.
a. CPU utilization and response time
b. Average turnaround time and maximum waiting time
c. I/O device utilization and CPU utilization

10. Consider a system implementing multilevel queue scheduling. What strategy can a computer user employ to maximize the amount of CPU time allocated to the user's process?

11. What is the meaning of the term busy waiting? What other kinds of waiting are there in an operating system? Can busy waiting be avoided altogether? Explain your answer.

12. Windows Vista provides a new lightweight synchronization tool called slim reader-writer locks. Whereas most implementations of reader- writer locks favor either readers or writers or perhaps order waiting threads using a FIFO policy, slim reader-writer locks favor neither readers nor writers, nor are waiting threads ordered in a FIFO queue. Explain the benefits of providing such a synchronization tool.

13. Explain the difference between internal and external fragmentation.

14. Compare paging with segmentation with respect to the amount of memory required by the address translation structures in order to convert virtual addresses to physical addresses.

15. Discuss the hardware support required to support demand paging.

16. Assume that you are monitoring the rate at which the pointer in the clock algorithm (which indicates the candidate page for replacement) moves. What can you say about the system if you notice the following behavior:
a. Pointer is moving fast
b. Pointer is moving slow

17. What are the advantages and disadvantages of a system providing mandatory locks instead of providing advisory locks whose usage is left to the users' discretion?

18. Some systems automatically open a file when it is referenced for the first time, and close the file when the job terminates. Discuss the advantages and disadvantages of this scheme as compared to the more traditional one, where the user has to open and close the file explicitly.

19. Discuss how performance optimizations for file systems might result in difficulties in maintaining the consistency of the systems in the event of computer crashes.

20. In what situations would using memory as a RAM disk be more useful than using it as a disk cache?

21. What is an operating system? What are the functions of an operating system? Have these definitions changed over time?

22. Discuss the trade-offs involved in choosing a time quantum in CPU scheduling. Does the choice of a good quantum depend on how the system will be used?

23. What are the differences between single-threaded vs. multi-threaded processes?

24. What is a batch file? What purposes does a batch file have?

25. Find a file system which you have used (like the NTFS used in Windows, for example), and describe some of its properties in terms of the concepts discussed in the text: for example, what attributes are stored per file, or what directory structure is used?

26. What is a VMware? How has it changed the landscape of desktops and servers?

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I have provided a brief explanation in the answer segment and I hope this information will help you. I have also referenced a few sources in order to give you a complete answer and provide you with detailed information as I saw necessary.

We will go through the questions one by one and I will provide you with a brief description of the answers and highlight all the important aspects you need to know about operating systems.

1. In a multiprogramming and time-sharing environment, several users share the system simultaneously. This situation can result in various security problems.
a. What are two such problems?
When we talk about multiprogramming, we are basically referring to several jobs in the pool where the operating system selects a job from the pool for the CPU to execute. One such problem in this environment is one user copying another user's data, alter it, steal it, or write over it. Another problem would be one user using another user's resources like memory space or printers at the expense of the first user.
b. Can we ensure the same degree of security in a time-shared machine as in a dedicated machine? Explain your answer.
We cannot ensure the same degree of security in a time-shares machine because they are less secure and the buffers in such systems overload easily. Additionally, a protection method designed by a human being can and will be broken into eventually, probably by another human being.

2. What network configuration would best suit the following environments? Explain your answers.
a. A dormitory floor
A dormitory floor -A LAN - because it is a small area and two or more computers connected together within the dormitory floor through hardware and software should be sufficient. With this configuration, computers can share files, resources, and if preferred, an Internet connection.
b. A university campus
A university campus - A LAN, A WAN if it is a very large campus
c. A state
A state -A WAN - since it is a large geographic area and will require the use of the internet for proper network configuration.
d. A nation
A nation -A WAN

3. Describe the five major activities of an operating system in regard to file management.
With regards to file management, the five major activities of an operating system include handling deadlocks, creating and deleting systems and user processes, synchronizing processes, communication of processes, and resuming and suspending processes.

4. What is the main advantage for an operating-system designer of using a virtual-machine architecture? What is the main advantage for a user?
A virtual machine will offer basic hardware that can be found in many other computers. Having a virtual machine takes away the need to have two systems, or to reboot to test its operating system. You are able to have multiple operating systems and boot the system only once. The system is easy to debug, and security problems are easy to solve.

5. Describe the differences among short-term, medium-term, and long term scheduling.
The Long-Term scheduler does not have to be fast, since it only needs to work when new processes are created. It has to be capable of scheduling I/O-bound and CPU-bound processes in order to make sure that the system is performing efficiently by keeping the Ready Queue and the I/O waiting Queue busy at all times.
Some system processes have to be swapped in and out of memory to keep a good combination of processes or to improve memory requirements. In this situation, the Medium-term scheduler would be responsible for scheduling the swapped processes.
The Short-term schedule decides the order in which the processes are executed. The Short-term scheduler needs to be extremely fast so it can keep the CPU working efficiently especially when processes are in the Ready Queue at all times, and where processes stay in the CPU for only milliseconds before they need I/O or are reschedule.

6. What are the benefits and detriments of each of the following? Consider both the systems and the programmers' levels.
a. Synchronous and asynchronous communication
"Synchronous communication is direct communication where the communicators are time synchronized. This means that all parties involved in the communication are present at the same time. This includes, but is not limited to, a telephone conversation (not texting), a company board meeting, a chat room event and instant messaging. Asynchronous communication does not require that all parties involved in the communication to be present at the same time. Some examples are e-mail messages, discussion boards, blogging, and text messaging over cell phones. In distance (specifically online) education asynchronous communication is the major (sometimes the only) method of communication. Usually, we use different discussion boards in each class with each having its own purpose." (Answers.com, 2010).

b. Automatic and explicit buffering
Automatic buffering provides a queue with an indefinite length so that the sender would never have to be blocked while waiting to copy a message. Explicit buffering specifies how large the buffer is. The sender may thus be blocked while waiting for a space to become available in the queue. Memory is less wasted with this kind of buffering.

c. Send by copy and send by reference
Send by copying denies the user receiver to alter the state of the parameter but send be reference allows it. The latter allows the programmer to write a distributed version of a centralized application by declaring the parameter as ...

Solution Summary

The solution answers 27 questions about the basic concepts of operating systems. Questions range from mutitasking to fragmentation to batch files and VMware.

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