Strategies Used For Page Replacement Computer Science Essay

Published:

Operating System (OS) is a computer hardware and software resources management procedures, also the core and foundation of the computer system. Operating Systems functions such as memory management and allocation, supply and demand determine the priority of system resources, control input and output devices, operation and management of network file systems and other basic services. Operating system is to manage all the hardware resources of computer system resources, including software and data resources; control procedures; improve the human-machine interface; provide support for other applications, so that all the resources of the computer system to maximize the role, to provide users with convenient Effective, friendly service interface. Operating system is a huge management control procedures, including the five aspects of general management functions: process and processor management, operations management, storage management, device management, file management. At present the common computer operating system DOS, OS / 2, UNIX, XENIX, LINUX, Windows, NetWare and so on. However, all of the operating system of concurrent, shared, virtual and uncertainty four basic characteristics.

Define Question 1:

Lady using a tablet
Lady using a tablet

Professional

Essay Writers

Lady Using Tablet

Get your grade
or your money back

using our Essay Writing Service!

Essay Writing Service

In the computer operating system, memory management, virtual memory paging, page replacement algorithm determines which page the page (swap out, write to disk), memory page allocation. When the page fails, the page can not be used to satisfy the free distribution of, or because there is no, or because the number of free pages is greater than a low threshold. 

When this is selected to replace and bring up a page reference to it must be paged again (read from disk), which relates to the I / O completion wait. This page replacement algorithm determines the merits of: net of other plug-in page, the better the algorithm of the time. A page replacement algorithm to provide the hardware to access the limited key information page, and try to guess which pages should be replaced, in order to minimize the total number of page faults, while balancing and cost algorithm itself (the main memory and processor time). 

Answer of Question 1:

The strategies used for page replacement:

Optimal Algorithm

The NRU (Not Recently Used) Page Replacement Algorithm

The First-In, First-Out (FIFO) Page Replacement Algorithm

Least Recently Used (LRU)

The Second Chance Page Replacement Algorithm

The Clock Page Replacement Algorithm

Optimal Algorithm

Algorithm replaces the reference page in the existing footer. Unfortunately, there is no way to determine which pages will be the last so in practice, the algorithm can not be used. It is measured as a benchmark against other algorithms can be useful, however.

Replace the page that will not be used for the longest time

Lowest page-fault rate of all algorithms

Requires advanced knowledge of page reference string

Useful for comparison studies

The best page replacement algorithm is easy to describe, but impossible to implement. It is such a moment, a page fault, some set of pages in memory, these pages will be in the next instruction (page contains the instructions) referred to in other pages may not be quoted until the 10, 100, or 1000 instructions , each page can be executed before the page with the first number of instructions to be referenced. 

Algorithm is simply the best web page, the page with the highest tag should be removed. If a page will not be used for 800 million instructions, another page will not be used for six million instructions, the first push to eliminate the error page, put it back to get as far as possible in the future. Computers and people, trying to delay as long as unpleasant as they can. The only problem with this algorithm is that it is impossible to achieve. 

The NRU (Not Recently Used) Page Replacement Algorithm

Nauru is divided into four categories in the algorithm R and M on the page of the state of the bit. From the lowest-level page, select the random numbers. The algorithm is easy to implement, but it is very rough. Better existence. 

To allow the operating system to collect information on what pages are being used and what is not, most computers use virtual memory for each page has two status bits associated with useful statistical data. R is set whenever the page is referenced (read or write.) M is set when the page is written (or modified). These bits are included in each page table entry, as shown. 4-0. It is important to realize that these bits must be updated for each memory reference, it is necessary to set up their hardware. Once a bit has been set to 1, it stays until the day the operating system software reset to 0. Class 0: not referenced, not modified.

Lady using a tablet
Lady using a tablet

Comprehensive

Writing Services

Lady Using Tablet

Plagiarism-free
Always on Time

Marked to Standard

Order Now

Class 1: not referenced, modified.

Class 2: referenced, not modified.

Class 3: referenced, modified.

The First-In, First-Out (FIFO) Page Replacement Algorithm

FIFO order to retain their tracks loaded into memory is stored in a linked list them. Remove the oldest web becomes negligible, but the page may still be in use, so the FIFO is a good choice.

Replace the oldest page

Maintain a current operating system in memory a list of all pages in the list of the most ancient one, and has recently arrived in the first page last page. Errors on the page, one at the head, the page is deleted, new pages added to the end of the list. When applied to the store, first in first out, you may cancel the mustache wax, but may also remove the flour, salt and butter. When applied to the computer the same problems. To this end, first in first out in its pure form is rarely used.

The latest replacement pages

FIFO scheduling algorithm into memory when the page has been chosen based on the page before the page into memory and then returns the data through memory. When the algorithm will need to enter the page has formed a queue, each team the home team to conduct the operation time of the memory.

Least Recently Used (LRU)

LRU is an excellent algorithm, but it cannot be implemented without special hardware. If this hardware is not available, it cannot be used. NFU is a crude attempt to approximate LRU. It is not very good. However, aging is a much better approximation to LRU and can be implemented efficiently. It is a good choice.

Replace the page that has not been used for the longest time

Requires a logical clock time for each page (LRU_TIME)

Or a stack of recent page references (LRU_STACK)

Or a list of all references (LRU_REF)

Same as OPT but on reverse of page reference string

Optimal algorithm looking backward in time

The Second Chance Page Replacement Algorithm

Second opportunity is to modify the FIFO, checks if a page will be removed before use. If so, the page can not be spared. This change greatly improves performance. Clock is a simple difference realization of a second chance. It has the same performance characteristics, but need a little less time to implement the algorithm.

A simple modification FIFO, to avoid throwing away a frequent problem with the web is to check the oldest page R-bit. If it is 0, the page and not use the old, so immediately replaced. If the R bit is 1, this bit is cleared, the list of web pages on the page at the end, although the loading time to update came just in memory. And then continue the search.

The Clock Page Replacement Algorithm

FIFO clock is more efficient than the version of a second chance, because the page does not have to constantly be pushed to the back of the list, but it is a second chance to perform the same general function. Clock algorithm to keep pages in memory, circulation lists, and "hand"(iterator) point to the list, the oldest page. When a page failure, there is no empty frame, then R (reference) bit is to check his hand position. If R is 0, then the new page is placed in the "hand " points, or R bit cleared the place page. Then, the clock hands increased, this process is repeated until the page is replaced.

Variants on Clock

Clock-Pro keeps a circular list of information about recently-referenced pages, including all M pages in memory as well as the most recent M pages that have been paged out. This extra information on paged-out pages, like the similar information maintained by ARC, helps it work better than LRU on large loops and one-time scans.

Define Question 2:

Operating system provides the basic mechanism of protection of computer processing. 60 years since the 20th century, operating system designers to explore how to create a "safe" operating system - the operating system mechanisms to protect the environment against an active adversary system. Recently, the importance of ensuring that security has become a mainstream issue for all operating systems. Review of past research, an overview of a secure operating system and research, such as system, to achieve the objectives and requirements of these requirements. For system design, to meet these requirements, we can see that software systems often results in implementation challenges, we are still exploring the complexities of today. However, if the system is not designed to achieve the security requirements of the operating system, its security features a myriad of ways the system failed. We have also studied the function of the operating system and security system reform after the initial deployment. In all cases, on the one hand, on the other hand lead to conflict between the security dilemma and the unwise compromises the potential function. We hope that system designers and implementers will learn about operating system security and effective implementation will be able to better understand how to manage the balance between functionality and security requirements. 

Answer of Question 2:

Security measures use to protect data and information in the computer

Lady using a tablet
Lady using a tablet

This Essay is

a Student's Work

Lady Using Tablet

This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

Examples of our work

Cryptography

Authentication

Access control

Security attacks

Attack prevention and security solutions

Cryptography

Encryption technology is the practice and research of information hiding. Intersection of modern cryptography mathematics, computer science, electrical engineering discipline. Encoding and decoding encrypted data, so that it can not be understood or interpreted by unauthorized persons. Data conversion by using the key encryption to encrypt the plaintext into cipher text. Application of cryptography, including ATM cards, computer passwords and e-commerce.

The types of Key Cryptography:

Secret key Cryptography

Public key Cryptography

Private key Cryptography

Secret key Cryptography

Secret-Key Cryptography is a Cryptography method where the same key is used for Encryption and Decryption. This leaves applications with the problem of how to securely exchange this key. This inherent problem of Secret-Key Cryptography has been solved by Public-Key Cryptography methods.

Public key Cryptography

Public-Key Cryptography is a Cryptography method where different keys are used for Encryption and Decryption. This is a major advantage over Secret-Key Cryptography and makes Public-Key Cryptography ideally suited for scenarios where secure key exchange is hard or impossible.

Private key Cryptography

As opposed to public-key cryptography, a cryptographic method in which the same key is used to encrypt and decrypt the message. Private-key algorithms include the obsolescent Data Encryption Standard (DES), triple-DES (3DES), the Advanced Encryption Standard (AES), also known as Rijndael, Blowfish, Twofish RC2, RC4, RC5 and RC6. A problem with private-key cryptography is that the emitter and the recipient of the message must agree secretly on a common key before hands.

Authentication

Authentication is the process of determining whether someone or something is, in fact, who or what it is declared to be. In private and public computer networks (including the Internet), authentication is commonly done through the use of logon passwords.

There are three types of authentication:

Password protection

Kerberos

Single sign-on

Password protection

A technology that allows the system login and password assigned tousers. File and directory protection, unauthorized access, requires the user to enter a password before access is allowed.

Kerberos

When users log on to the Kerberos system, the password is encrypted and sent to Key Distribution Center (KDC) authentication service. If authentication is successful, the KDC creates a master ticket, sent back to the user's machine.

Single sign-on

Recognition system, allowing users to login with a user name and password for multiple sites Internet. Single sign-on systems are also used within the enterprise, allowing users to access the local use the same user name and password, all authorized network resources.

Access control

The management of admission to system and network resources. The first part of access control is authenticating the user, which proves the identity of the user or client machine attempting to log in. The second part is granting the authenticated user access to specific resources based on company policies and the permission level assigned to the user or user group.

Access control can be divided into:

Models

Policies

Mechanisms

Models

Enables to control the ability of a process to access securable objects or to perform various system administration tasks.

Policies

Specified by the users on the type of privilege to the objects assigned to them by the database administrator.

Mechanisms

Refers to the method which the system implements the security policy.

Security attacks

Security attack refers to a process whereby a person compromise your computer by installing harmful malicious software in your computer without your knowledge. These malicious software includes viruses, spywares, adwares, and Trojan horses. These software often deletes certain vital files on your computer, making your computer to function abnormally, spying on your online surfing habits, and cause advertisements to pop up on your screen when you are online.

The types of Security attacks:

Cryptanalysis

Viruses and worms

Denial-of-service attack

Software exploitation

System penetration

Cryptanalysis

The art of recovering original data (the plaintext) that has been encrypted (turned into cipher text) without having access to the correct key used in the encryption process. When new encryption algorithms are introduced, cryptanalysis determines how hard it is to break the code.

Viruses and worms

Definition of Worm:

A program that makes copies of itself; for example, from one disk drive to another, or by copying itself using email or another transport mechanism. The worm may do damage and compromise the security of the computer. It may arrive in the form of a joke program or software of some sort.

Definition of Virus:

A program or code that replicates; that is, infects another program, boot sector, partition sector, or document that supports macros, by inserting itself or attaching itself to that medium. Most viruses only replicate, though, many do a large amount of damage as well.

Denial-of-service attack

An assault on a network that floods it with so many additional requests that regular traffic is either slowed or completely interrupted. Unlike a virus or worm, which can cause severe damage to databases, a denial of service attack interrupts network service for some period. A distributed denial of service (DDOS) attack uses multiple computers throughout the network that it has previously infected. The computers act as "zombies" and work together to send out bogus messages, thereby increasing the amount of phony traffic.

Software exploitation

It is a piece of software, a chunk of data, or sequence of commands that takes advantage of a bug, glitch or vulnerability in order to cause unintended or unanticipated behavior to occur on computer software, hardware, or something electronic (usually computerized). This frequently includes such things as gaining control of a computer system or allowing privilege escalation or a denial of service attack.

System penetration

Is a method of evaluating the security of a computer system or network by simulating an attack from a malicious source, known as a Black Hat Hacker, or Cracker.

Attack prevention

Are network security appliances that monitor network and/or system activities for malicious activity. The main functions of 'intrusion prevention systems' are to identify malicious activity, log information about said activity, attempt to block/stop activity, and report activity

The security solutions:

Firewalls

Intrusion detection systems

Antivirus software

Security patches

Secure file system

Firewalls

Computer security system, control data from one computer or network traffic to another. The main purpose of a firewall is to protect the private network from users from the external network to directly access, especially through the Internet resources. The internal private network may also be prohibited direct access to external computer. To do this, all communications are via a "proxy server " to determine whether a message or file will be allowed to enter or exit the private network.

Intrusion detection systems

Intrusion Detection System (IDS) is a device or software application, monitoring network and / or malicious activities or violations of the policy system activity, and generate reports management station. The implementation of intrusion detection intrusion prevention and detection of possible events trying to stop the process. Intrusion detection and prevention systems (IDP) may be the main focus is to identify the events, record information about them, tried to stop them, and report to the security administrator.

Antivirus Software

Anti-virus or anti-virus software is used to prevent, detect and remove computer viruses, worms and Trojan horses. It may also prevent and eliminate adware, spyware and other forms of malware.

Security patches

Patch is a software design and problem solving, or update its computer programs or data support. This includes fixes security holes and other vulnerabilities, improve availability and performance.

Secure File System

SFS (Secure File System) is a plan to create and manage encrypted disk volume number set, and the DOS and Windows.

Conclusion & Recommendation:

Refer to the answer Question 1 & Question 2, we can know how important are Page replacement and security in the Operating System. Identify the difficulty in the page replacement design and propose the adaptive replacement solution in the page replacement. In the security, we can know security is the ongoing process of exercising due care and due diligence to protect information, and information systems, from unauthorized access, use, disclosure, destruction, modification, or disruption or distribution. The never ending process of information security involves ongoing training, assessment, protection, monitoring & detection, incident response & repair, documentation, and review. This makes information security an indispensable part of all the business operations across different domains.