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For this assignment, Im going to explain about page replacement, computer virus and how prevent from being attacked by viruses. Before that I would like to explain about operating system. The operating system acts as a mediator between application programs and computer hardware even though the application is normally executed directly by the hardware. Microsoft Windows, and GNU/Linux and Mac OS X are some examples of popular modern operating system for personal computers. Operating system can be found in a device that contains a computer for example, video game consoles to supercomputers and also web servers.
Page replacement is an optimizing instruction or algorithm that a computer program can follow to manage a collection of information stored on the computer. When the storage is full, the algorithm must decide which items to remove to make space for new ones. So, page replacement is a vital element of virtual memory implementation in most current universal reason operating system. Plus, this allows user to use disk storage for data which doesn't fit into physical random access memory. The latency of storage describes how long the cache can return a desired item after requesting it. The hit rate of storage describes how often a search history is actually found in the cache. Less usage information usually will be tracked by faster replacement strategies, to reduce the quantity of time takes to update the information. Each replacement strategy is cooperation between the hit rate and latency. These following are the strategies.
The first strategy is Belady's Algorithm. This is the most capable caching algorithm will always discard the unnecessary information in future. Next is Least Recently Used or LRU. This LRU functions as it discards the least recently used items first, this algorithm keep tracking when what was used. The third strategy is Most Recently Used or MRU. MRU is the same as LRU that it discards the least recently used items first. So, when a file is being constantly scanned reference pattern. In fact, MRU will be the best replacement algorithm.
The forth is Pseudo-LRUF. For collections with a large associative, carrying out cost of LRU becomes too high. So if a method that always discards one of the LRU items is satisfactory, the PLRU algorithm can be used which just require one bit per collection item to work. Next is Random Replacement. This RR acts as it randomly picks a candidate item and discards it to build free space when it is needed. Plus, this algorithm does not keep any information about the access record. It is already used in ARM processors and it is a capable stochastic motivation.
The sixth is SLRU that stands for Segmented LRU. For this one, SLRU collection is divided into two parts, a protected part and a probationary part. The lines in each parts are ordered from the newly accessed end of the probationary part. In protected part, hits are removed from anywhere they currently added to the most recently accessed end of the protected part. Lines in protected part have as a result been accessed at least twice and the protected part is fixed.
Next, 2-Way set associative is intended for high-speed CPU collections where even PLRU is time-consuming. The address of a new item is used to analyse one of two possible locations in the collection where it is authorized to go. The LRU of the two is discarded. To indicate which of the least recently used, it requires one bit per pair of collection lines.
Direct-mapped Cache is intended for the highest-speed CPU collections where even 2-way set associative are slower. The address of the new item is used to analyse the one site in the collection where it is authorized to go. Everything that was there before is discarded. Next, Least Frequently Used counts how frequently an item is required. Those that are used least frequently will discard first. For Adaptive Replacement Cache, it regularly balances among LRU and FLU, to develop collective result.
Lastly, Multi Queue Caching Algorithm is for considering other things such as item with a different cost where it acts as it keeps the item which is costly to get, items that taking up more collections as the collections may discard a large item to provide spaces and ttems that expire with time as the computer may discard the expired items. A variety of algorithm also exists to retain cache coherency. This applies only to state where many independent collections are used for the same data.
Computer is an electronic device that is used by people all over the world. Even though the computer a one of the greatest technology ever made by human, it does not mean that it is always safe to use to do our daily activity such as online, gaming, transaction, online payment and etc. This is because computer has a virus that can that can infect a computer. Computer virus can be classified as computer program. By infecting files on a network file system, virus can spread itself to other computers. It can also copy itself and fill the computer hard disk space. There are many types of virus such as Malware, Trojan horses, worms, spyware, and other nasty software. Trojan horse is not a harmful program but it hides bad functions. For worms, it can develop security vulnerabilities to spread automatically to the other computers through networks. Viruses, Trojan horses and worms can damage computer system performance or data or both. Spyware can appear when we are on the internet. It acts as it collects small pieces of information about users without their knowing. The software is hidden from the user and the user will not be noticed. To detect the spyware will be difficult.
Exploit is software that can cause unwanted actions to occur in computer software, hardware and other computerised device and as a result payload appears. This is because it is caused by the virus that is executed by the exploit on computer where the payload of a virus will cause a movement, changing, and deleting files. These threats are raised by downloaded files from internet. Sending emails are also one of the raiser.
For computer user, these viruses can be prevented because there are many ways to keep a computer safe. One of the steps is to have a firewall. It is an element of a network or a computer system. It is designed to block all the unofficial contacts while permitting the official communications. For different types of circumstances, there are different types of security management. Home can be considered as a small area. So it only needs an essential security while large organizations will need high maintenance and advanced software and hardware to avoid malicious attacks from hacking and spamming. Plus, it is highly recommended to keep firewall on in a computer to avoid others from having even a single contact with the computer. To detect and remove viruses, it is recommended that user must have basic antivirus software or a unified threat management system. The antivirus software must be up to date we have to install the security protection earlier to help to protect the computer from new viruses and spyware programs.
For more security, use must sets up a password with a difficult combination of number and letters to prevent an unauthorized user from getting the password. If it is not in use, user should always log off the computer. Also, user must use a robust password when using a wireless connection. The default SSID network name should be changed and don't forget to disable the broadcast. MAC address filtering should be enabled if the user wants to keep track of all home network MAC devices connecting to the router. User should also assign STATIC IP addresses to network devices and also disable the ICMP ping on router. Next, always remember to review firewall log to spot any unusual network connections. For more security, the guest account to avoid someone access to the information stored in computer.
Next, medium businesses should use a fairly strong firewall or unified threat management system where it should be installed and they must use a password that is difficult to be broken and remember to update it every month. Increase knowledge about physical security to employees. A strong firewall and proxy is needed for a large business to help prevent unwanted people from breaking into the secret information.
Next, make sure that a strong antivirus software and Internet Security Software package is installed. Prepare and use network analyzer or network monitor when needed. To maximize security, increasing security guards could use a little help. For more information, Data Loss Prevention (DLP) is a system that is designed to detect and avoid the unofficial use and transmission of confidential information and some organizations use this system as the protection of network. Always remember to perform regular maintenance by scanning the computer most of the time. There are many ways to help ourselves prevent the virus from attacking and damaging our computer system.
For question 1, page replacement is a progression where a computer can store up and recover data from secondary storage for use in main memory. The advantage of paging is that it makes space by deleting unwanted or useless items from the computer.
For question 2, computer virus can attack anytime when we are not prepared. There are many ways to protect our computers. Many strong antivirus is provided by antivirus company. We must always careful whenever we are surfing the internet because the viruses may spread easily without protection.
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Author Unknown. Year of Publication (Unknown). Paging. Available: http://en.wikipedia.org/wiki/Paging. Last accessed 08-02-2011.
Author Unknown. Year of Publication (Unknown). Payload (Software). Available: http://en.wikipedia.org/wiki/Payload_(software). Last accessed 06-02-2011.
Author Unknown. Year of Publication (Unknown). Cache Algorithm. Available: http://en.wikipedia.org/wiki/Cache_algorithms. Last accessed 06-02-2011.
Author Unknown. Year of Publication (Unknown). Network Security. Available: http://en.wikipedia.org/wiki/Network_security. Last accessed 08-02-2011.