The Goals Of Operating Systems Computer Science Essay

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Different personality have different views base on operating system. To a college student operating system is software that allow to access internet. To programmer operating system is software that makes it possible to implement programs on the computer. To user of application package software that makes easy to use the package. The main aspect of operating system is software that interact user of a computer and computer hardware.

The operating system has many goals. The main goal is efficient use. The operating system ensures efficient use of memory, CPU and input output devices. Operating system can consume CPU and memory resources that can consume overhead. Besides, operating system monitors use of resources to make certain of efficiency. The second goal of operating system is user convenience. To make user comfortable to done their task. Operating system ensures user friendly interfaces such as GUI (Graphical User Interfaces). It makes that user easy to done their task. Furthermore, noninterference in the activities of its user. User can face interference in computational activities. The operating system also prevents illegal file access because the system knows which data can access by whom. Only the authorize user can access the data.

1. Page replacement is where the system must decide which page in main memory should be replaced or removed in order to make room for new pages. This can be done by over-writing / modifying the memory space. List and explain in detail all he strategies used for page replacement.

Page replacement is one of the concepts in demand paging. If page fault occurs and no free page frames exists in memory. When no free page available page replacement becomes necessary. Page replacement also prevents over-allocation of memory by modifying page fault service routine to include page replacement. For page replacement modify (dirty) bit is use to reduce overhead of page transfers. In addition, modified pages only written to disk. Page replacement is a separation between logical memory (Random Access Memory) and physical memory (hardware). They are many strategies used for page replacement; such as page fault frequency, FIFO. The following diagram is an example of page replacement.

The strategies that used for page replacement are many but some are not frequently using. LRU (Least Recently Used) also a strategy that used for page replacement. LRU is an automatic choice for development in a virtual memory handler because it possesses the stack property. However, LRU page replacement is impossible because most computer systems do not provide sufficient use bits in PIT entries to store the time of last reference. LRU strategy uses the principle of locality of reference as the basis for its replacement decisions. The performance of LRU page replacement can describe as followed. At every page fault the LRU page is replaced by a new page. The page table entry of page records the time when the page was the last referenced. This information is initialized when a page is loaded, and it is modified every time the page is referenced. When a page fault occurs, PIT is searched to locate the page whose last reference is earlier than that of every other page. This page is replaced with the new page.

Optimal page replacement is a page replacement that implies making page replacement decisions in such a manner that the total number of page faults during the execution of a process is the minimum possible, no other sequence of page replacement decisions can lead to a smaller number of page faults. To archive optimal page replacement, at each page fault the page replacement policy should give attention to all alternative page replacement decisions, analyze their implications for future page faults, and then select the best alternative. Optimal page replacement is infeasible because the virtual memory handler does not have knowledge of the future behavior of a process. However, it provides a useful basis for evaluating performance of other page replacement policies.

First In First Out page replacement also known as FIFO page replacement. At every page fault the FIFO page replacement policy replaces the page that was loaded into memory earlier than any other page of the process. To facilitate FIFO page replacement, the PIT entry of a page is used to record the time when the page was last loaded into memory. When a page fault occurs, this information is used to determine, the page that was loaded earlier than any other page of the process. This page is replaced by the required page.

In the nut shell, page replacement is one of the concepts in demand paging. They are many type of page replacement such as random page replacement, second chance page replacement. These page replacements are used base on memory needs by the file. They page replacement is important when the memory need.

Question 2

2. Name and explain all the security measures that can be taken to protect data and information in the computer or being exchanged in a network.

Answer (2)

Security is a measure taken as precaution against theft or sabotage. Security is a treat to resources from nonusers. Security has few goals. The goals are can classify as four. The first thing is secrecy. It means the authorized user only able to access information. Besides that, privacy also a one of the goal of computer security. The data should be used for the purposes for which it is intended and shared. Other than that, authenticity is that should be possible to verify the source or sender of information and also verify that the data is preserved in the form in which it was created or sent. Moreover, the integrity also a goal that should impossible to ruin or corrupt. The treat can be classify as two that internal factor and external factor. Following diagram show that factors:

The are many treat when we share our information via network. We have to take few security measures to prevent our information and computer. The treat that mostly harm our computer and our information is virus. They are many viruses like Trojan, Worms. The measure we have taken is few only. But it helps us to prevent our computer and the information. First thing we need to follow is do not open any attachments from unknown persons. Besides that, when receive unknown mails or attachments delete it. If download any files from internet before copy that file scan it by anti-virus program. Besides, don't simply save the downloaded file into additional memories like pan drive; copy the file to hard drive and scan it before run it. Furthermore, if receive greeting cards or any jokes from unknown person don't open it or run it launch it to view. The final thing that has to do is keep updating the anti-virus software. This is because there are many new viruses are releasing via network so old version anti-virus software cannot detect and delete the virus so we need to update the antivirus software.

Other than virus, hackers also a famous treat that harm our computer and our information. To prevent hackers we need to take the same security measures to prevent virus like install anti-virus program. Besides that, we need to update all software that in our computer. Set up automatic update help us to update the program. This is because in the software have many viruses. Furthermore, install trusted software only. If you do not understand the software or if u not needs the software don't install it. Moreover avoid PZD file sharing software. This software used for movies. If you don't know about this kind software doesn't install it. In addiction using complex password login also prevent the hackers. Other than that, run antivirus scan regularly. Turn on install the firewall. It may help o prevent the hackers.

Some programs help us to prevent the treats. One of the programs is spyware and adware removers. Spyware is a program that placed on a computer without user's knowledge hat secretly collects information about the user, often related to web browsing habits. Spyware can enter a computer as a virus or as a result of a user installing a new program. The spyware communicates information it collects to an outside source while you are online. Adware is a program that displays online advertisement in a banner or pop-up window on web pages, e-mail, or other internet services. Sometimes, spyware is hidden in adware. A spyware remover is program that detects and deletes spyware and other similar programs. An adware remover is a program that detects and deletes adware. Some operating systems and anti-virus program include spyware and adware removers.

In the nut shell, the network helps us to share information fast. It also efficient way to share information via network. Share data or information via network has some negative effects. If we taken effective security measures help us to protect our computer and our private data. The most effective way is installing antivirus program in our computer.


Operating system is set of programs containing instructions that work together to coordinate all the activities among computer hardware resources. In the operating system I learnt many things. Operating system make user comfortable with computer. Without operating system make user difficult to use computer. Besides that, the operating systems using user friendly items like using GUI. Besides that, I have learnt the security measures that can take to protect our information and computer. By doing this assignment, I learnt the objective of operating system. Besides that, the advantage of operating systems. This assignment helps me upgrade my knowledge about operating system.