Oracle date
An Oracle DATE stores the date and time to the second. An Oracle TIMESTAMP stores the date and time to up to 9 digits of subsecond precision, depending on the available hardware.
Both are implemented by storing the various components of the date and the time in a packed binary format. From the Oracle Concepts Guide section on dates
Oracle uses its own internal format to store dates. Date data is stored in fixed-length fields of seven bytes each, corresponding to century, year, month, day, hour, minute, and second.
You can use the DUMP() function to see the internal representation of any particular date (or any other value for that matter), but that's probably more than you need (or want) to know.
Apparently, not in form of millisecs.
Which actually makes sense, since they do not have any running operations on current date/time:
http://www.ixora.com.au/notes/date_representation.htm
http://infolab.stanford.edu/~ullman/fcdb/oracle/or-time.html
No. DATE is a timestamp value with seconds precision. You need TIMESTAMP(3) to store milliseconds.