Virtual Memory: Definition, Components, And Working

What is Virtual Memory?

Discuss about the Observations and Opportunities in Architecting.

The idea of creating logic space in the memory location of a machines is known as virtual memory. The logical space in machines respectively corresponds to the physical spaces located in the system (Vesely et al., 2016). The mapping of the logical spaces in to the physical spaces are done by a process known as dynamic mapping.The virtual memory stores the virtual or the logical addresses for the systems and provides the systems with the virtual storage facility which helps them in the storing the temporary data in the system logically and deleting the data when the requirement of the data is over. It also keeps the process of the operating systems safe as they prevent a process to directly read or write the contents of a particular process without prior permission from the system. The procedures of the virtual memory arte done by a unit known as the memory management unit present in the CPU of the system.This helps the system in maintaining a proper balance in the system and provides efficient options for the operating system for the allocation and re-allocation of memory to the process that requires it. This report consists further discussion of the procedures and the components of the virtual memory.

There are various components of the virtual memory among which the three are notably the major elements of the virtual memory.  These are Main Memory (RAM), Secondary Memory (Disk) and the Page Table.  The main memory holds the recent chucks of the data in the system and secondary memory stores those chunks in the system. These are those which are not currently being used by the system (Chi et al., 2016). The page table holds the location of the data in the system. The most recently used data are stored in the main memory. The pages are used for the storage of data and each of these pages are subdivided into frames which stores the data after dividing them and allocating them to the respective blocks. The size of a frame is similar to that of a frame. The first frame always indicates towards the address 0x00000000 to 0x00000FFF. The second frame always indicates towards the address 0x00001000 to 0x00001FFF. In situation where the physical memory is of 256 Mbs, the last addresses would basically range from the 0x0FFFF000 to 0x0FFFFFFF. The address range generally covers the 4096 bytes. Another important concept to consider during the discussion of virtual memory is that of frame number. Basically the first frame number is always indicated with a 0 and second frame has frame number 1 and so on. The main memory can be considered basically as the fast storage and the pages that the currently working with the system, overall can be easily considered as the storage system that performs the function of a cache memory.

Components of Virtual Memory

The disk memory is basically the storage system that helps in the storage of the pages that are currently not required by the system. Whenever the system looks for a page the appropriate page is brought from the secondary memory and transferred to the main memory which would be performing the functions for the system. The addresses of the memory are stored in the secondary memory (Wilkins et al., 2016). The processor generally fetches the address from the main memory and is redirected to the secondary memory where it finds the required addresses and the data in them and then again sends it to the main memory. In addition to this, in case a page is modified the corresponding modification is also done in the secondary memory of the system. The secondary storage can be thought of the as the long term storage for the system.

The page table is used for keeping track of the pages of the systems and also the properties of the pages are stored in the directories of the page table. The systems make an update to the page table in case the system wants the page table alter and modifies the pages and makes an update accordingly. In addition to the pages there are entries in to the pages for the storage of data in the system and these entries are stored in the system into the virtual address space after being indexed. For the storage of the pages in the page table the 2ⁿ number of entries are made so that n number of indexes are required in the page table.

For the application of virtual memory is done generally in the entry of the page numbers in the indexes of the page table (Seshadri et al., 2016). The component which is being discussed in this area of the report is the page table. The virtual memory and the physical memory are generally not required to have an extensive relation among themselves although they work correspondingly with each other for the processor to process the data and make changes accordingly. Hence, the bit operators are used for searching the addresses required for the system and the operators would be indicating the requirement of the bits and provide the location of the addresses in the virtual memory. The valid bits are used for the indication whether the memory is available or not. It also provides a clear indication of whether a memory has to be fetched from the secondary memory or it is already available in the main memory. When the pages are fetched from the main memory the valid bit is set to 1 and in case the page is overwritten and the page is no longer required by the process the valid bit is set to 0. In addition to this, there is the dirty bit, which indicates weather the memory has been updated or the it has the same contents as of before. In case the memory has been update and the update has been discarded the system must perform the write back operation to take the memory into its previous state. In case the update the update has not been set to the memory a dirty bit is set to 1 until the update to the main memory is done and the bit is again set to 0 once the update is done. This helps a great deal in speeding up the system and making efficient updates to the storage system of the machine. Whenever a page is loaded into the memory the dirty bit of the page is set to 0. In case any type of write instruction is performed on the system the dirty bit is set to 1.

Working of Virtual Memory

Access control is the process that is used for the protection of the memory in the system. This helps in indicating the weather a user can read, write or delete a particular part of memory in the system. This helps in preventing programs from harming the data of the other and processes and the procedures of the data are not hampered by this. Additionally, the frame number helps in helps in indicating about location of the frame in a particular page. The disk location helps in determining the exact location of the data. In case the user wants to the update of delete the data the user has to have knowledge of the disk location of the data in system. In a sense quite similar to the frame number.

The concept of virtual memory has a huge development in the field of information technology. There concepts of the virtualization and cloud computing has developed from these concepts and there has been a huge improvement in these fields also (Mijumbi et al., 2016). In the future the users would no longer require to store the data in the physical storage systems of the personal machines. This is also expected to extend to the enterprises as well. The cloud architecture developers have developed data centres which would be storing all the important data required for the clients. This help in backup and recovery process of the data for the clients.

How to change Virtual Memory Size in Windows 10 ... Retrieved from https://mywindowshub.com/customization-virtual-memory-size-windows-10-technical-preview/

If Windows virtual memory is too low, you can increase it ... Retrieved from https://www.pcworld.com/article/2840886/if-windows-virtual-memory-is-too-low-you-can-increase-it-but-there-are-trade-offs.html

Johnson, B. Professional visual studio, 2015.

Operating System - Virtual Memory - Tutorials Point. Retrieved from https://www.tutorialspoint.com/operating_system/os_virtual_memory.htm

Optimize Windows for better performance - Windows Help. Retrieved from https://support.microsoft.com/en-us/help/15055/windows-7-optimize-windows-better-performance

What is virtual memory? - Definition from WhatIs.com. Retrieved from https://searchstorage.techtarget.com/definition/virtual-memory

Conclusion

For conclusion it can be said that the Virtual memory is one of the most efficient concepts that has been developed over the years and this has helped a great deal in the development of the process of the operating system in the machines of the users. It helps in addressing a number of issues of a system and performs the process of memory management and memory updating procedures. This paper has provided the description of the virtual memory in the systems and components associated with it. Additionally, the description of the page table component of the virtual memory has been discussed and future trends which are associated with it.

References

Chi, P., Li, S., Xu, C., Zhang, T., Zhao, J., Liu, Y., ... & Xie, Y. (2016, June). PRIME: a novel processing-in-memory architecture for neural network computation in ReRAM-based main memory. In ACM SIGARCH Computer Architecture News (Vol. 44, No. 3, pp. 27-39). IEEE Press.

Mijumbi, R., Serrat, J., Gorricho, J. L., Bouten, N., De Turck, F., & Boutaba, R. (2016). Network function virtualization: State-of-the-art and research challenges. IEEE Communications Surveys & Tutorials, 18(1), 236-262.

Seshadri, V., Pekhimenko, G., Ruwase, O., Mutlu, O., Gibbons, P. B., Kozuch, M. A., ... & Chilimbi, T. (2016). Page overlays: An enhanced virtual memory framework to enable fine-grained memory management. ACM SIGARCH Computer Architecture News, 43(3), 79-91.

Vesely, J., Basu, A., Oskin, M., Loh, G. H., & Bhattacharjee, A. (2016, April). Observations and opportunities in architecting shared virtual memory for heterogeneous systems. In Performance Analysis of Systems and Software (ISPASS), 2016 IEEE International Symposium on (pp. 161-171). IEEE.

Wilkins, V. V., Fallone, R. M., Meyer, A. T., & Boyle, W. B. (2016). U.S. Patent No. 9,268,499. Washington, DC: U.S. Patent and Trademark Office.