## How Do Multimedia Timer Settings and System Time Resolution Affect GetSystemTimeAdjustment Results?

Understanding GetSystemTimeAdjustment Results on Windows 7

Question 1: Relationship between Time Queries and System Time Update Intervals

Yes, your assumption is correct. If the system time is synchronized periodically, querying the system time should either result in no change or a change that is a multiple of the increment retrieved by GetSystemTimeAdjustment.

Question 2: Discrepancy in Time Adjustments

The difference in your testing results can be explained by the following:

• Actual System Time Update Period: GetSystemTimeAdjustment does not provide the actual update period of the system time. Instead, it reports the interval at which the system clock is adjusted if time synchronization is configured.
• Resolution of System Time Queries: GetSystemTimeAsFileTime provides the system time with a resolution of 100 nanoseconds. However, the actual system time update period (obtained via NtQueryTimerResolution) is typically around 15.625 milliseconds (100 nanoseconds * 156,250).
• Effect of Multimedia Timer Interface: The multimedia timer interface (timeBeginPeriod) can set the timer period to values not obtainable through NtSetTimerResolution. This can influence the actual update period of the system time.

Summary:

GetSystemTimeAdjustment reports the interval for time adjustment, while NtQueryTimerResolution should be used to obtain the actual update period of the system time. Discrepancies in results can occur due to differences in resolution and the influence of multimedia timer settings.

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