Virtual versus Physical Memory

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You can almost always add physical memory to a computer with positive results. Memory is the single most significant factor in overall system performance. Adding more memory may not be possible in the short term for several reasons: the cost of upgrading can be a barrier, or the system may not have any space to quickly add additional memory chips.

There are alternatives to purchasing more memory. After Windows NT has been tuned to make the best use of its current memory levels, modifying the location and size of the pagefile may have an effect on the system.

The pagefile is defined using a minimum and maximum size on a given hard drive. On a system with several hard drives, moving the pagefile to a drive that is faster or not used as much improves read and write requests. Placing the pagefile on a drive other than the operating system can result in problems during a memory dump. Memory dumps cause the information in physical memory to be stored in the pagefile during a crash. If the pagefile is on a different drive from the operating system, the dump will not be successful.

When the system starts, a pagefile is created at the minimum level. The operating system increases the size of the file to accommodate demand up until the maximum level is attained. You can monitor the current usage of the pagefile in Performance Monitor and the Task Manager. Growing the pagefile requires system resources and may result in a fragmented pagefile. These factors affect system performance. The minimum size of the pagefile should be large enough to accommodate current uses.

Another technique is to create additional pagefiles stored on different drives. The read/write operations may be handled faster. This depends of the current activity on the drives and the drive’s own performance issues. Windows NT supports one pagefile on each logical disk. Placing pagefiles on multiple logical drives contained on the same physical disk does affect system much. Because there is only one physical reader on each physical disk, it takes longer to read.

You can make all changes to the pagefile from the Performance tab of the System properties. Select the Change button in the Virtual Memory section. See Figure 6.21 for details on virtual memory assignment.

The maximum size of the pagefile could be left intact. The recommendation is to always keep a 50 MB buffer between the minimum and maximum sizes. This buffer ensures that the pagefile can grow to accommodate short-term demands.