I knew about this, but didn’t know it was public!
Source: http://support.microsoft.com/kb//931975
… In SQL Server 2005 and in SQL Server 2000, the SQL Server database engine uses the following two forms of timer to generate time information:
- High-resolution timer
- Low-resolution timer
In the high-resolution timer, the timer resolution is based on the Read Time-Stamp Counter (RDTSC) instruction of the CPU. In the low-resolution timer, the timer resolution is based on the GetTickCount function in the Microsoft Windows API.
… When you use Transact-SQL statements to perform time calculations that are based on system-provided date and time functions, you must carefully investigate the statements. Specifically, if you have written DST times in hard code in the application logic, the DateDiff and DateAdd system functions are not DST aware.
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