A SMALL OVERVIEW OF SYSTEM VIRTUAL MEMORY AND WINDOWS PAGING CONCEPTS
Computer performs and completes its operations with help of memory. There are two types of memory available in the physical system. They are,
· Random Access Memory (RAM ) – Main Memory
· Virtual Memory
Random Access Memory is the physical chip that is located in the hardware of the system that can act as a memory location. This is the part of Primary storage device of the system. The data cannot be permanently stored in chip. All data’s will be erased as soon the Physical system gets powered off. The memory can also be called as Main Memory.
Virtual Memory is a stimulation of physical RAM and is stored in the secondary storage of the system. Hard disk will act as a secondary storage for the system. This technology helps to extend additional memory capacity and work with RAM to load applications. The virtual memory will reduce the cost of expanding the capacity of physical RAM. The implementation of virtual memory will diff for operating systems, but the basic concept is same.
If an application opens it first load the data into the free address locations of the RAM (physical memory) and the processor communicates with the RAM to fetch the data for the further processing. As RAM is a physical memory location, the speed for the communication, storage function and its process are very fast compared to the virtual memory. The virtual memory works with the help of secondary storage device and its speed is low compared to the physical storage location (RAM).
Consider a scenario that a system is not configured with virtual memory and is only using the physical memory to complete its works. Such a configuration cannot handle multitasking or multiprocessors. If we open one application it will be loading into the available free space of the RAM and hence there will be no space available to load the second application. The second application needs to wait until the first applications to be closed free up the RAM space. By implementing additional RAM for the system will create room for the second application to occupy the RAM space, but is required additional cost. There will also be a limitation to install the physical RAM on the physical system.
To overcome the situation scientists developed the virtual memory method, where the less or not frequently used data from the RAM will be moved to the Hard disk virtual memory location and thus free space in RAM for the processing of the new data. If an application requires a data that is stored in the virtual memory, it is then transferred back to the RAM for the process. Paging is an important part of the virtual memory implementation that in most contemporary general-purpose operating systems, allowing them to use disk storage for data that does not fit into physical random-access memory (RAM).
An adequate amount Memory is needed for the smooth and reliable functioning of the Operating system. The RAM and virtual memory is added together to give the total memory size for the system. The applications that are requires heavy memory module for their functioning only see the total allocated memory size of the system.
The movement of data from RAM to virtual memory and vice versa is called ad thrashing. The data follow is taken care automatically by the operating system without manual intervention. This transfer of data will create slowness in the performance of the operating system. We can analysis the data transfer from the continuous blinking of Hard disk LED or we can understand it from the noise from the Hard disk head movement through the platter.
In Windows, virtual memory uses Paging.sys file to process its operations. By default the Pagefile is located in the root directory of the operating system. We can tweak the performance of the pagefile using the Windows Advanced virtual memory setup. This can be access from,
My Computer -> Properties -> Advanced -> Settings -> Performance Options -> Advanced -> Change
Windows default configuration for the paging file size is to automatically expand its size, but it will consume more hard disk space in case if the application crashes, more utilization of virtual memory or due to memory leaks. This functionality also causes heavy fragmentation of the data that is written in the paging file, as it expands without limit. The result will be slowness in the performance of the operating system.
These settings also have an advantage that, the operating system can automatically increase the paging file when required without the interaction of the Administrators. This helps to reduce slowness of the system in time of heavy usages.
The System Managed size can be set by selecting the radio button to the System Managed Size tab. Thus system will take control of the paging file and thus increase or decreases its usage accordingly.
The custom settings will limit the growth of the paging file size. In normal condition to tweak the performance of the system and the usage of the hard disk space we use custom settings.
The recommend custom setting for the paging file configuration is to set the Initial size as 1.5 times larger of the total physical memory of the system and the Maximum size is 2.5 times larger of the total physical memory.
Locking of the paging file size will helps to make a control on the hard disk capacity. If the system primary partition is not having a sufficient amount of space, setting a limit is very useful.
No Paging File
This setting will not create a paging file in the system and thus virtual memory mechanism will not be functioning for the particular operating system.
The functionality can also be used to reconfigure the paging file from one disk drive to another eg: C drive to D drive.
· We cannot leave the paging file configuration blank for the primary boot partition. The partition from where the Windows operating system boots because to create a memory dump file during the time of operating system crash a small amount of paging file to be configured in the primary partition. The crash report is first written into the paging file and on the first booting after the operating crash the recorded data is written into memory dump file “memory.dmp”.
· The paging file settings for an operating system is purely depends on the operating system, applications that running, the total amount of physical memory, mode of implementation etc.
· Defragmentations tools can be used to keep arrange of the fragmented paging file blocks in the hard disk and thus improve the system total performance. The tools such as PageDefrag are used for the defragmentation of the paging file.
· The data which are written in the paging file is in unencrypted format. There are tools available for encrypting the data that are writing on the paging file eg: TrueCrypt – Free Open-Source Disk Encryption tool.
· The paging file configurations can be located from the registry location (Start->Run->regedit), editing the values will change the present paging file configuration.
· Paging file will be emptied at the time of normal reboot and all the written contents in the Pagefile (pagefile.sys) will be get cleared. If you need not want the pagefile to be cleared, we need to set that in the registry value “ClearPageFileAtShutdown”.
· The paging file settings cannot be applied soon as we set the configurations; it required a system reboot to implement the paging file settings.
– Melbin Mathew
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