Important Characterstic Of Operating System Computer Science

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In this term paper we are traveling to analyze a really of import characterstic of operating system i.e Memory Management, how the memory is managed between assorted operations, procedures

We began with brief description about memory direction system. .In this term paper we will be much focused n how this system works instead than comparing its architecture & A ; construction

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Memory direction is the bosom of runing systems ; it is important for both scheduling and system disposal. So we should be much bothered by its workin and how really it works and how it is

Memory direction in Microsoft Windows runing systems has evolved into a rich and sophisticated architecture, capable of scaling from the bantam embedded platforms where Windows executes from ROM all the manner up to the multi-terabyte NUMA constellations, taking full advantage of all capablenesss of bing and future hardware designs.

Linux implements the practical memory informations construction merely like UNIX. Virtual memory country constructions are maintained in linked lists by it. These informations constructions represent uninterrupted memory countries which are incorporating the same protection parametric quantities.


Memory direction system is of import portion of each operating system. The chief map of this system is to pull off the memory system of random entree memory and the other storing devices which are available on the system. Main undertakings that come under the memory direction are allotment and deallocation of memory to the assorted procedures running on the system. The memory direction system should be optimized as its map affects the velocity and the public presentation of the operating system.

Memory direction system provides the undermentioned characteristics:

Large Address Space

The memory direction system shows the user that big memory infinite is available alternatively of the existent memory it has. Virtual memory is many times greater than the physical memory of the system.


Every procedure of the system is provided the practical reference infinite. These address infinites wholly differ from each other so the procedures running on one application plan non impact the other. The hardware besides protects the practical memory country from composing. Thus codification and information is protected from acquiring overwritten by knave applications.

Memory Function

Memory function is used to map image and information files into a procedures address infinite. In memory function map, the contents of a file are linked straight into the practical reference infinite of the procedure.

Fair Physical Memory Allocation

The memory direction subsystem allows each running procedure in the system a just portion of the physical memory of the system

Shared Virtual Memory

Virtual memory is the chief and an of import portion of the memory direction system. The memory demands were turning that ‘s why the practical memory was introduced. So plans were developed that made the semblance that system has big memory to be allocated to the procedures. The meats provide the installation to utilize the secondary storage devices to carry through the excess demands of the memory.

Some function maps are at that place for the practical memory map to work. These maps are responsible for the reference interlingual rendition that converts the practical references to the physical addresses..

Virtual memory map by and large use the paging or cleavage as per the demand of the operating system.


In paging both the reference infinite the practical and existent is divided into fixed size pages. The pages are manipulated and is placed at different topographic point in difficult disc and the physical memory. The memory direction unit does the reference interlingual rendition by utilizing the page. The address page tabular array

specifies the mapped physical pages and the practical memory pages. The memory direction unit changes the practical memory reference to the physical memory reference dwelling page frame figure and the beginning in that page. It besides provides the functionality to use protection on the page. Virtual memory takes the big reference infinite in comparing to physical memory. With each practical page a spot is associated with the page tabular array to look into if the page is present anyhow or non. If the page is non there a page mistake exclusion is generated. It is handled by the package which place the pages required back to the physical memory from the difficult disc and mistake is generated if it is invalid


Both the operating systems have the modern operating systems and have a batch of common characteristics in between them. Some of the similarities in both of the memory direction system are-

Hardware Abstraction Layer:

Both the operating systems have the hardware abstraction bed that is non system dependent. Thus the meats are enabled to be coded independently.

Transcript on write: –

If the pages are shared same transcript of the page is used between the procedures. But if an single procedure makes any alteration in the page that is made private to that procedure merely, therefore increases the efficiency.

Memory Management


Windows on 32 spot x86 systems accesses upto 4GB of physical memory. This is because that the processor ‘s reference coach which is 32 lines or 32 spots can merely entree reference scope from 0x00000000 to 0xFFFFFFFF that is of 4GB. Windows provides 4Gb logical infinite for each process.. The lower 2GB is for the user manner procedure and upper 2GB is reserved for Kernel manner codification of the Windows. This operating system uses paging characteristic for pull offing the memory

Paging allows the package to utilize a logical memory reference than the physical memory reference.

Windows provides an independent, 2 GB user reference infinite for each and every application ( procedure ) in the system. To the application merely 2 GB of memory is appeared to be available than the entire memory available. When an application requests more memory than the available memory, Windows NT satisfies the petition by paging noncritical pages of memory-from this and/or other processes-to a page file and liberating those physical pages of memory. Thus a planetary pile exists for no long in the Windows NT. Every procedure gets the private 32-bit reference infinite from which all of the memory for the procedure is allocated-including codification, resources, informations, DLLs ( dynamic-link libraries ) , and dynamic memory. The system is still limited by whatever hardware resources are available, but the direction of available resources is performed independently of the applications in the system.


Linux implements it memory informations i.e practical informations same as UNIX. practical memory country constructions are maintained in linked lists by it. These informations constructions represent uninterrupted memory countries which are incorporating the same protection parametric quantities. This list is searched when a page is to be referred for a location i.e known or we can state for exact location. This besides records the scope of reference that is acquiring mapping onto & As ; protection manner besides whether it has been in memory as non page-able and besides specifies the way whether in upward or downward way. This besides stipulate if that is a public or a private location If in instance the entries increases than a 32, so tree is formed instead than associate list.This attack is best in all most of the state of affairss

Process Address Space: –

Both the operating system distribute the procedure practical reference infinite in the same manner. Higher portion is used by the meat and lower by the lower portion. The meats portion all procedure point to the same meat codification. So now as procedure shift is concerned, we need to exchange the lower page enteries, whereas as upper portion can be remained untasted. In Linux there is infinite of in ratio 3:1 that is 3 sarin for procedures to utilize and 1 sarin for meat to excute its operations whereas in instance of Windowss this is an equal ratio of 2:2 that is 2gb, 2gb for both procedures and meats


The window system is really complicated one. Windows for bringing the pages use a clusted demand paging attack, and for the page replacing Window uses a clock algorithm attack

In clustered demanding attack there is demanding of pages merely when they are required, besides when Windowss even demand for pages the window bring bunch of 1-8 pages at one time harmonizing to present province of the system or Air Combat Command to the required scenario

The assorted page mistakes received by meats –

A protection misdemeanor has occurred.

A shared page has been written.

The stack needs to turn. in.

These mistakes are largely non recoverable. The 3rd merely one efforts to read compose merely that page someplace else and do the new one read/write. In this manner the copy-on-write plants.

The clock algorithm used by Windows is local. When a page mistake occurs, and blaming procedure ‘s working set is below a minimal threshold, so the page is merely added to the working set.

On the other manus, if the working set is higher than one another threshold, so it reduces the size of working set. Hence the algorithm can be called planetary.

But the system does make some planetary optimisations excessively. For illustration, it increases the working set of procedures that are doing a big figure of page mistakes, and diminishing the working set for those who do non necessitate adequate memory. Alternatively of merely working when there is a page mistake, merely like Unix,

Windows has a daemon yarn working excessively, but called in this instance as Balance Set Manager. This is invoked every 1 second, and it checks whether there is adequate free memory. If there is non, so it invokes the working set director. The working set director maintains to maintain the free memory above threshold. It checks the working sets of procedure from old and large to the immature and little. And depending on how many page mistakes they have generated, it increases or decreases them. If a page ‘s mention spot is clear, so counter associated with the page is incremented. If the mention spot is set, the counter is set to zero. After the scan, pages with the highest counter are removed from the working set. Thus, the planetary facet of this clock algorithm is given by this working set director.

Windows divides the list of pages into four lists:

1. Modified Page List

2. Stand-bye Page list

3. Free Page list

4. Zeroed Page List


The Linux Virtual memory merely concentrate on the fact that it is to be simple and has less operating expenses. Therfore it has many jobs when used under heavy burden processes. It uses a demand paging. that excessively even with non pre demanding characteristic.Before the linux version 2.2, this O.S used NRU Algorithm for page replacing but due toits a batch of jobs and defects, the made a new attack that was Lru ( leasr late used ) an approximated aaproach. The effectness of anging procedure to LRU is done by increasing the age of a page by a changeless when the page is found to be referenced during a scan. Least Recently Used ( Lru ) is approximated reasonably in this

This Virtual Pages Are divided into 4 lists in Linux system

Active List

Inactive dirty List

Inactive clean List

Free List

For Linux 2.4, the dynamicity was introduced for inactive list Now in this system automatically make up one’s mind how many figure of pages t maintain in this memory in the as per given state of affairs. And besides

Decide the unactive pages to maintain in the memory or non in any given state of affairs

Another optimisation nowadays in the Linux Kernel, is that they now recognize uninterrupted I/O, i.e. they now decrease the precedence of the page “ behind ” and so that page becomes a campaigner for eviction Oklahoman. The page devil in Linux is kswapd which awakens one time a 2nd, and frees memory if adequate is non available


Both the systems are originated in different backgrounds –

Windows was created taken in history to maintain Commercial Settings and

Whereas Linux taken in history for Hackers.

Both are every bit of import as per the environment and demands of the user

Both have many similar maps and operations merely with a few differences

Windows is developed with motive and it has gone through more attempt in its design and development.

In instance of Linux, the determination is taken favoring simpleness.over its public presentation

Therefore the Windows is developed into sophisticated, complex codification whereas Unix is simple and elegant but still modern. The consequence of which is that Windows has more characteristics but is hard to keep and better from the developers, while Unix has less characteristics but is easier to keep and develop. Windows is likely to give better public presentation while on occasion crashing

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