# Counter Types

Each counter is assigned a counter type. The counter type determines how the counter data is calculated, averaged, and displayed. The Performance console supports more than 30 counter types, although many of the available counter types are not implemented in the counters installed with Windows 2000.

This section describes all supported counter types, including the following information.

**Counter type name** The name of the counter type. The System Monitor counter descriptions in this Help file include the name of the counter type. You can click the counter name in the description to see a definition of the counter.

**Description** A brief description of the counter type, including a description of the formula by which counters of that type are calculated and displayed.

**Generic type** The general category that represents the display format counter. Generic types include:

- Average. These counters measure a value over time and display the average of the last two measurements.
- Difference. These counters subtract the last measurement from the previous one and display the difference, if it is positive; if negative, they display a zero.
- Instantaneous. These counters display the most recent measurement.
- Percentage. These counters display calculated values as a percentage.
- Rate. Similar to an average counter, these counters sample an increasing count of events over time and divide the cache in count values by the change in time to display a rate of activity.

**Formula** Describes how to convert the raw data and other components, such as performance frequency, to arrive at the formatted counter value for display in the Performance console. The variables N and D appear in the formula to describe the two distinct data components, such as raw data and performance frequency, used to calculate the displayed counter values.

For each counter type, the notation of the formula can include the following variables:

Variable | Description |
---|---|

B | A base-value variable. Some counter types require the use of a counter base that supplies a stored value for calculating their formatted value. That base value is the denominator in the formula for the counter type. When describing counter types with multiple samplings, B is shown with numbered subscripts, such as B0 for the oldest sampling, B1 for the next more recent sampling, and Bn for the latest sampling. |

N | The numerator, typically the first variable. For the purposes of the calculation formulas in this section, N is used to describe the raw counter data. |

D | The denominator, typically the second variable, as needed. |

The following table describes the types of counter bases and the counter types that they support.

Base Type | Description | Corresponding Counter Types |
---|---|---|

PERF_AVERAGE_BASE | Stores the denominator for calculating a counter to present "time per operation" or "count per operation." | PERF_AVERAGE_BULK PERF_AVERAGE_TIMER |

PERF_COUNTER_MULTI_BASE | Indicates the number of items sampled. It is used as the denominator in the calculations to get an average among the items sampled when taking timings of multiple, but similar items. | PERF_100NSEC_MULTI_TIMER PERF_100NSEC_MULTI_TIMER_INV PERF_COUNTER_MULTI_TIMER PERF_COUNTER_MULTI_TIMER_INV |

PERF_RAW_BASE | Stores the denominator of a counter that presents a general arithmetic fraction. | PERF_RAW_FRACTION |

PERF_SAMPLE_BASE | Stores the number of sampling interrupts taken and is used as a denominator in the sampling fraction. The sampling fraction is the number of samples that were 1 (or TRUE) for a sample interrupt. | PERF_SAMPLE_FRACTION |

**Average** The mathematical formula used to calculate averages of the formatted counter data.

**Example ** An example of the specified counter type. Click the counter name in the example to see a description of that counter.

Additional information pertaining to how System Monitor formats raw data, such as data size and display suffix, appears in the Platform SDK.

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