Operating Systems And Software - Virtual Memory

Exam: CompTIA 220-701 - CompTIA A+ Essentials 700 series

Explain the process and steps to install and configure the Windows OS. Virtual Memory

Virtual memory makes a program think that it has contiguous address space, when in reality, the address space can be fragmented and often spills over to a hard disk. RAM is a limited resource, whereas virtual memory is, for most practical purposes, unlimited.

There can be a large number of processes, each with its own virtual address space. When the memory in use by all the existing processes exceeds the amount of RAM available, the operating system moves pages of information to the computer's hard disk, freeing RAM for other uses. In Windows, virtual memory is known as the paging file, specifically pagefile.sys that exists in the root of C:. To view this file you need to unhide it. This can be done in

Windows Explorer by clicking Tools on the menu bar and then selecting Folder Options. In the resulting Folder Options window, click the View, then look for the Show Hidden Files and Folders button, which you'll need to click. Once done, move just below this button and uncheck the box for the Hide Protected Operating System Files option. Pagefile.sys should now show up in the root of C:.

Take a look at the size of your page file and jot down what you find. To modify the size and location of the page file, open the System Properties window, and click the Advanced tab. Next, click the Settings button within the Performance box; this will bring up the Performance Options window. Now, click the Advanced tab, and click Change in the Virtual memory box. From here you can let Windows manage the virtual memory for you, or select a custom size for the page file. The paging file has the capability to increase in size as needed. For a long time with Windows XP/2000 computers, the rule was that the page file would have an initial size of 1.5 x RAM, and a maximum size of 3 x RAM, but the page file can be increased beyond that if necessary.

This rule might not be used on today's computers for a variety of reasons; however, running a number of programs at simultaneously can be made easier by increasing the page file size in order to maximize the computer's performance. Another option would be to move the page file to another volume on the hard drive, or to another hard drive altogether. It is also possible to create multiple paging files, or stripe a paging file across multiple disks to increase performance. Of course, nothing beats adding physical RAM to the computer, but when this is not an option, possibly because the motherboard has reached its capacity for RAM, optimizing the page file might be the solution. For more information about configuring virtual memory in Windows XP, see the following link: http://support.microsoft.com/kb/314482. Some of the techniques listed apply to Windows Vista as well.