Performance Monitor is the principle tool for monitoring system performance and for identifying the location of the bottleneck. To start Performance Monitor, click Start, click Control Panel, click Administrative Tools, and then double-click Performance Monitor. Here is a summary of some important counters and what they tell you:
- Memory, Committed Bytes:
This counter is a measure of the demand for virtual memory.
This shows how many bytes were allocated by processes and to which the operating system has committed a RAM page frame or a page slot in the pagefile (or perhaps both). As Committed Bytes grows greater than the available RAM, paging will increase, and the pagefile size that is being used will also increase. At some point, paging activity starts to significantly affect performance.
- Process, Working Set, _Total:
This counter is a measure of the virtual memory in “active” use.
This counter shows how much RAM is required so that the virtual memory being used for all processes is in RAM. This value is always a multiple of 4,096, which is the page size that is used in Windows. As demand for virtual memory increases beyond the available RAM, the operating system adjusts how much of a process’s virtual memory is in its Working Set to optimize available RAM usage and minimize paging.
- Paging File, %pagefile in use:
This counter is a measure of how much of the pagefile is actually being used.
Use this counter to determine whether the pagefile is an appropriate size. If this counter reaches 100, the pagefile is full, and things will stop working. Depending on the volatility of your workload, you probably want the pagefile large enough so that it is generally no more than 50-075 percent used. If much of the pagefile is being used, having more than one on different physical disks, may improve performance.
- Memory, Pages/Sec:
This counter is one of the most misunderstood measures.
A high value for this counter does not necessarily imply that your performance bottleneck stems from a shortage of RAM. The operating system uses the paging system for purposes other than swapping pages because of memory over-commitment.
- Memory, Pages Output/Sec:
This counter shows how many virtual memory pages were written to the pagefile to free RAM page frames for other purposes each second.
This is the best counter to monitor if you suspect that paging is your performance bottleneck. Even if Committed Bytes is greater than the installed RAM, if Pages Output/sec is low or zero most of the time, there is no significant performance problem from insufficient RAM.
- Memory, Cache Bytes,
Memory, Pool Nonpaged Bytes,
Memory, Pool Paged Bytes,
Memory, System Code Total Bytes,
Memory, System Driver Total Bytes:
The sum of these counters is a measure of how much of the 2 GB of the shared part of the 4-GB virtual address space is actually being used. Use these to determine whether your system is reaching one of the architectural limits.
- Memory, Available MBytes:
This counter measures how much RAM is available to satisfy demands for virtual memory (either new allocations, or for restoring a page from the pagefile).
When RAM is in short supply (for example, Committed Bytes is greater than installed RAM), the operating system will try to keep a certain fraction of installed RAM available for immediate use by copying virtual memory pages that are not in active use to the pagefile. Therefore, this counter will not reach zero and is not necessarily a good indication of whether your system is short of RAM.