SQL Kiwi (5/5/2012)

Datetime values are no more "associated" with a float value than they are with any other type that can be implicitly converted (see the conversion table in Books Online - CAST and CONVERT (Transact-SQL)). The internal representation is two integers - one for the number of days from the base date, and one for the number of ticks (1/300th second) since midnight. In fact the second format seems to be 0.003 second time intervals, rounded to 0, 3, or 7 in the third decimal place when used:

DECLARE @dt datetime = '1900-01-02 00:00:00.006';

SELECT @dt;

SELECT CONVERT(binary(8), @dt);

My biggest concern with this question though, is that it encourages people to be sloppy with types and relies on hidden implicit conversions. As a general rule, try to be explicit about types in T-SQL code.