Performance Monitor Counters

Performance Monitor doesn't really count anything. Its counters collect, average, and display data from internal counters by using the Windows NT Registry and the Performance Library DLLs. The internal counters are part of the computer hardware.

Performance Monitor collects data on various aspects of hardware and software performance, such as use, demand, and available space. You activate a Performance Monitor counter by adding it to a chart or report or by adding an object to a log. Performance Monitor begins collecting data immediately.

Note

When you select a counter in any view, Performance Monitor collects data for all counters of that object, but displays only the one you select. This causes only minimal overhead, because most of Performance Monitor's overhead results from the display.

This book refers to counters by associating them with an object in the following format:

Object: Counter

For example, the % Processor Time counter of the Process object would appear as

Process: % Processor Time

to distinguish it from Processor: % Processor Time or Thread: % Processor Time.

Tip

Click the Explain button in the Add To dialog box to display the definition for each counter. The Explain button works only when you are monitoring current activity, not logs.

There are three types of counters:

• Instantaneous counters display the most recent measurement

For example, Process: Thread Count displays the number of threads found in the most recent measurement.

• Averaging counters, whose names include per second or percent, measure a value over time display the average of the last two measurements. When you start these counters, you must wait for the second measurement to be taken before any values are displayed.

For example, Memory: Pages/sec, shows the average number of memory pages found in the last two reads during the second measured.

• Difference counters subtract the last measurement from the previous one and display the difference if it is positive. If it is negative, they display a zero.

Performance Monitor doesn't include any difference counters in its basic set, but they might be included in other applications that use Performance Monitor, and you can write them yourself. For information on writing performance counters, see the Win32 Software Development Kit.

Some hardware and applications designed for Windows NT come with their own counters. Many of these extensible counters are installed automatically with the product, but some are installed separately. In addition, there are a few specialized counters on the Windows NT Resource Kit 4.0 CD that you can install. See your product documentation and Performance Monitor Help for detailed instructions on adding extensible counters.