Free Essay


In: Computers and Technology

Submitted By carline
Words 960
Pages 4
Operating Systems Concepts

Contents Introduction 3

Virtual Memory 3

First In First Out 4

Least Recently Used 5

References 6

As we gain a better understanding of how computers and their operating systems work, we are able to better grasp how they handle the execution of programs. As we first learn to use computers we really do not think about the things that programs need in order to run, such as memory, as long as everything works. Although as we advance our knowledge of how such things operate, we begin to understand the mechanics of such things as physical and virtual memory.
Virtual Memory Normally when we think of memory, in terms of computers, we generally tend to think about things like the hard drive or the RAM. These items are generally used in the storage of programs, documents and multimedia, however when it comes to running a program their functions are slightly altered. Programs that are executed to run on a computer require a certain amount of memory in order to run. As modern operating systems have become capable of running multiple processes, or programs, with limited resources of memory, operating systems need a way to manage these resources. This is referred to as memory management, which allocates the memory resources as they are needed. When a memory manager has the capability to allocate the memory resources to multiple programs this is known as virtual memory. Virtual memory is a technique that is used to give the illusion of addition memory when a system is low on physical memory, the manager would divide the available space into pages and then stores its contents in mass storage. When paging is used, the processor divides the linear address space into fixed-size pages that can be mapped into physical memory and/or disk storage. When a program or task references a logical address in memory, the processor translates the address into a linear address and then uses its paging mechanism to translate the linear address into a corresponding physical address. Windows is known to use paging where Linux, Mac OS X, Solaris and Amiga OS 4 uses file swap. The process is, swapping which is the moving of memory pages between RAM and disk. By default Windows OS configuration, 2 GB of this virtual address space are designated for each process’ private use and the other 2 GB are shared between all processes and the operating system.
As an example of this I have found a program that emulates the process that memory management goes through when it allocates memory to a program. Once you press start, there are roughly 8 processes that are taking turns in requesting the use of the systems memory resources. All of the processes start out as light blue, once the programs start the ones that begin to request resources turn dark blue. There are also 16 pages of virtual memory along with 8 pages of primary memory.
The virtual memory is yellow while the primary memory starts out as white, as they are currently empty. Once a process request resources it will randomly chooses a page, as the virtual memory is brought into primary memory. If a process request a page that is already in use the process goes from green to yellow, indicating that its contents have been changed and that the original contents have been saved before the page is used by another program. This is an excellent example of what the memory manager does to maintain computers resources, for multiple programs.
First In First Out
First in first out, or FIFO, it allows for a process keeps running on a CPU until it is blocked or terminated. The main advantage of the FIFO policy is simplicity, as the oldest pages are always replaced. The FIFO also provides a certain degree of fairness, since requests are served in order. However, the main disadvantage is that short jobs can get stuck behind long running jobs. As well as the fact that the pages which are being deleted does not mean that it is not in use, as pages that are accessed more frequently may be replaced. Constantly doing this could be considered bad judgment.
Least Recently Used
Least recently used, or LRU, replaces the page which has been unused for the longest time, as well as the primary memory that has gone the longest time used. LRU maintains a linked list of all pages ordered from the most recently used to the least recently used. Maintaining a list on every instruction execution is very expensive and time consuming.
In relation to the last two methods discussed, I have found a simulation that best emulates these methods. It simulates 16 pages of virtual memory along with 8 pages of primary memory, I then inputted a sample set of numbers and then set it to sample string. Once I pressed start the LRU and FIFO went through the string of numbers, as they did they proceeded to go through the number of page faults, number of page references and percentage of page faults. The number of page faults went from one to eight, as the numbers went up the page references and fault numbers increased as well. As a clicked on fast and slow the number of reference pages steadily increased, as the percentage of page faults fluctuated wildly between numbers. This is caused by the fact that as the number of page faults and references increases the percentage of fault or dropped pages changes as some go unused or was in service for long periods of time.

William Stallings 6th Edition, Operating Systems internals and Design Principles, Chapter 7 and 8
Page replacement algorithm information retrieved from…...

Similar Documents

Premium Essay

Gender in Busisness

...| Final Paper | BMGT 312 Gender in Business | | Antoinette | 12/14/2012 | | A friend of mine was promoted to a managerial position. He assumed the position from a woman of foreign background that allowed her representatives(both male and female) to skip pass their immediate supervisors and come directly to her with any office or personal problems, from office grievances to attendance issues. Instead of “six degrees of separation” she also would invite these employees over for dinner and drinks. This relationship has continued on to her new position, whereas, whenever the representatives are in disagreement with his style of management they tend to confront her with it to insure that their wants/needs are addressed accordingly. Although he and the former manager are on amicable terms, he had to assert himself to his subordinates to make them understand his position and his policies. Communication Hearing Robert talk about the issues he was having with the staff, I reminded him to remember when he encountered a new boss who was trying to make a name for himself and how their initial reactions were - probably don’t bother me with trivial issues - and you felt that you were not getting anywhere, so you revert back to what/who you know. Communicating to your staff with what your expectations are and what’s acceptable and what’s not is one step to correcting the problem. He needed to communicate to his assistant manager’s to what their roles are and how to...

Words: 2002 - Pages: 9

Premium Essay

Busisness Management

...Management vs Leadership The article I chose came from and is entitled “Leader or Manager, what does your small business need?” by Marc Compeau (see link at the bottom). The article discusses the constant debate of what is better for a business; a manager or a leader? The book defines a manager as “planning, organizing, leading, and controlling of human and other resources to achieve organizational goals efficiently and effectively” (P.5). The book described leading as being able to “motivate. Coordinate, and energize individuals and groups to work together to achieve organizational goals” (P.8). In the definition the book states that to manage you must lead. Compeau states “I do know that your business has different needs at different times.” I personally believe that you need to be able to do both obviously, but it is not about wearing two hats, it is about knowing when to wear which hat! This is an extremely rare combination very few can achieve. Compeau offered his own distinction between the two; Leadership is managing change, Management is leading stability. You cannot just manage, managing keeps everything the same and nothing is moving or growing. Leading is changing and moving forward. This is why having a strong “managing leader” would help a business to strive. Compeau also discusses employees needing direction. The book states that “Leadership revolves around encouraging all employees to perform at a high level to help the organization achieve...

Words: 391 - Pages: 2

Free Essay

Busisness Analytics

...Unit 4    [GB513: Business Analytics]    Assignment This assignment requires you to use Excel. There is no template for this assignment. Make sure you explain your answers and provide the regression output tables for questions 1 and 2. Question 1 Shown below are rental and leasing revenue figures for office machinery and equipment in the United States over a seven-year period according to the U.S. Census Bureau. Use these data to run a linear regression and then forecast the rental and leasing revenue for the year 2012. Year Rental and Leasing ($ millions) 2004 5,860 2005 6,632 2006 7,125 2007 6,000 2008 4,380 2009 3,326 2010 2,642 Question 2 Suppose a researcher gathered survey data from 19 employees and asked the employees to rate their job satisfaction on a scale from 0 to 100 (with 100 being perfectly satisfied). Suppose the following data represent the results of this survey. Assume that relationship with supervisor is rated on a scale from 0 to 50 (0 represents poor relationship and 50 represents an excellent relationship), overall quality of the work environment is rated on a scale from 0 to 100 (0 represents poor work environment and 100 rep resents an excellent work environment), and opportunities for advancement is rated on a scale from 0 to 50 (0 represents no opportunities and 50 represents excellent opportunities). Answer the following questions: A) What is the regression formula? B) How reliable do you think the estimates will be based on this formula?......

Words: 709 - Pages: 3

Premium Essay

Intro to Busisness

...Which economic system is best suited for handling a crisis of epic proportions (hurricane, flood, blizzard, forest fire, etc.)? Why? A socialist system is the best economic system to handle emergency situations. First, let’s understand what a socialist society is. “A socialism society is where the state owns certain productive resources. The government manages efforts to minimize dramatic differences between economic classes, and opportunities are given to entrepreneurs, with varying degree of restrictions.” “It lies somewhere between communism and capitalism, with a fairly high degree of government planning and some government ownership of capital resources.” (Bovee) “All individuals have access to basic articles of consumption and public goods to allow for self-actualization. Large-scale industries are collective efforts and thus the returns from these industries must benefit society as a whole.” [] A socialist system can help a country concentrate efforts and resources to an emergency. One of the most important disaster response strategies of a socialist society is to mobilize the entire country to help disaster areas. They can launch a general mobilization and send soldiers to the disaster area shortly after an emergency. The government will help everyone equally. In addition to government efforts, individuals and organizations can provide assistance to the affected area. They can send use their own......

Words: 510 - Pages: 3

Free Essay


...Journal of Small Business and Entrepreneurship. An Empirical Investigation Of Causes Of Failure In Small Business And Strategies To Reduce It. 4 (3), P18 John L. Colley (2007) Principles of General Management The Art and Science of Getting Results Across Organizational Boundaries. United State Of America : Yale University Press.P298 Suzy,W Denise,W. (2014). Agile woe compounds China's property problems. Available:,agile-woe-compounds-chinas-property-problems.aspx. Last accessed 02/Nov/2014 Jerry Pradier (2009). Financial Success: Ten Shortcuts to a Profitable Business. Canada: Business development network ,LLC. Content 4 James Burrow, Brad Kleindl. (2012). Project My Own Business. In: Busisness Management. 13th ed. USA: Cengage Learning, 2012. P52 X. (2009). THE CHALLENGES OF GROWING A BUSINESS - AND HOW TO MEET THEM. Available: Last accessed 09/Nov/2014. Wong, ZaChary (2010). Human Factors in Project Management. San Francisco: Jossey-Bass A Wiley Imprint. Creating Content,Air Cover for The Team Kevin Uphill, Alex McMillan (2007). Buying and Selling a Business for Wealth. London: Thorogood Publishing. P27. 8)eter Cohan. (2009). After 101 years, why GM failed. Available: Last accessed 4/12/2014. Zachary Silver. (2013). Is GM's recovery......

Words: 2512 - Pages: 11

Free Essay

Successfully Enterpreneure

...productive under changed circumstances.” The BRAC Centre has a department for disaster management and climate change, which was set up two years ago with money donated from the Gates Foundation. It has also built many cyclones shelters and plans to build many more in the future, as cyclones will become more frequent. Over the last 30 years, BRAC has gone from strength to strength. BRAC currently operates in 69,000 villages in Bangladesh and it provides assistance to around 110 million people. He regards his employees as the reason behind BRAC’s success. He says, “There is a can-do culture at BRAC. We have an edge over many organisations; particularly those in the non-profit sector.” He adds, ” We prize efficiency. We are run more like a busisness, with targets to be achieved, although there is no bottom-line in the sense of a profit motive. But in everything we do there are targets, whether it is to reduce child mortality rates or increase the numbers of children attending school.” He also added “We also train our people well. BRAC has 20 training centres across Bangladesh and at any given time there are 4,000 people being trained.” Another reason for his optimism about the future is his strong faith in the Bangladeshi character. Countries where BRAC operates • Asia: Bangladesh, Afghanistan, Sri Lanka, Pakistan • Africa: Uganda, Tanzania, Southern Sudan, Liberia, Sierra Leone • America: Haiti • BRAC provides technical assistance to organizations in Haiti, India,......

Words: 3977 - Pages: 16

Premium Essay

Sme Towards Implementation of Gst

... The first case is, when its base is substantially different from the base of the old tax. Second, even a revenue neutral GST imposed on the same base as the old tax could trigger a pattern of price changes that is quite different, leaving the net impact on the price level uncertain (though possibly small). Third, prices could rise as a consequence of the widening of margins by traders seeking to protect themselves from the (yet) uncertain effects of a new tax. Finally, even if the GST eliminates elements of multiple-taxation inherent in the current sales and services taxes, the positive impact may not always be passed fully to consumers by way of lower prices. It is reasonable to expect that the impact of the GST on prices in SMEs busisness in Malaysia will mirror more closely the experiences of developing rather than developed countries. Awidely-cited study on the price effects of the VAT or GST surveyed 36 countries — of which 21 cases were developing economies. In the developing countries sample, the tax was found to impact only negligibly on the consumer price index (CPI) in 14 countries (or 66.7% of the sample). In another four cases (19%), the tax triggered a clear, one time (permanent) increase in the price level. In three cases (14.3%), expansionary wage and credit policies were already in place and so the tax was suspected of merely accelerating inflation. Taken at face value, the study suggests that in an economy not already facing inflationary pressures, the...

Words: 5991 - Pages: 24

Free Essay

Business Plan

...Business plan Smith Warehouse Las Catalinas Mall P. O. Box 362 Caguas, Puerto Rico 00726-0362 Telephone (787) 555-7755 Fax (787) 555-7756 E-Mail Table of Contents I. Table of Contents 2 II. Executive Summary 3 III. General Company Description 4 IV. Products and Services 5 V. Marketing Analysis 7 VI. Operational Plan 8 VII. Busisness Risk and Options 11 Executive Summary Thanks to the development of the web and its incremental use, Smith Warehouse has decided to create an online supermarket with delivery. “No waiting in line, no wasting of time”. Our business allows you to compare prices across the largest Grocery and Health & Beauty products in the PR. Visit our website; you're guaranteed to find the best prices, all the offers and the best value. General Company Description is a shopping website will serve as guide for the best offers and best buys for food prices. It will allow you to compare the value and prices of your entire cart, comparing with others retailers in the PR. It automatically checks what's in your basket and recommends swapping items for ones of better valued products. You can choose from five different departments: * Grocery * Produce * Dairy * Health & Beauty * Wines & Beers How much can you save? You can save up to 35% on the total of your shopping’s.   Ways to Save * Personal Shopping Companion Bar - Get the best value for your cart...

Words: 2272 - Pages: 10