Introduced in SQL Server 2008 : DateTime and DateTime2

DateTime and DateTime2

The datetime2 datatype was introduced in SQL Server 2008 along with the date and time datatypes.
Unlike the datetime datatype in SQL Server, the datetime2 datatype can store time value down to
microseconds and avoids the 3/1000 second rounding issue.
The precision with a datetime2 is upto 100 nanoseconds.

DECLARE @dt AS DATETIME
SET @dt = GETDATE()
SELECT @dt

DECLARE @dt2 AS DATETIME2
SET @dt2 = GETDATE()
SELECT @dt2

As you can see, when using the datetime datatype is rounded to increments of .000, .003, or .007 seconds.
However the datetime2 has a larger date range, a larger default fractional precision, and optional
user-specified precision. The precision scale is 0 to 7 digits, with an accuracy of 100 nanoseconds.
The default precision is 7 digits.

Moreover datetime2 supports a date range of 0001-01-01 through 9999-12-31 while the datetime type
only supports a date range of January 1, 1753, through December 31, 9999. The timerange as mentioned
earlier in case of datetime is 00:00:00 through 23:59:59.997
whereas in datetime2 is 00:00:00 through 23:59:59.9999999.