what is 'packed numeric data'?

You can specify in SQL*Loader that something like this :

123456789
123456789
123456789
123456789

is really 3 sets of numbers (one for each column in you table), as in...

123 456 789
123 456 789
123 456 789
123 456 789

by telling it at what positions in the file that each column in the table begins at.

Is that what you meant?