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    int systemUptime = GetTickCount();    // was Environment.TickCount

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dwTime in Type: DWORD The number of milliseconds that have elapsed since the system was started. This is the value returned by the GetTickCount function.

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Summary

The GetTickCount API

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static extern uint GetTickCount();

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static extern uint GetTickCount();

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Private Shared Function GetTickCount() As UInteger

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    public static extern long GetTickCount();

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        long entryTick = GetTickCount();

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        while ( GetTickCount() < (entryTick + delay) )

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Documentation

[GetTickCount] on MSDN