As I write the word lists for the curriculum, I have been exploring the derrivatives for each word. It amazes me how far knowing one root, whether it be an English, Latin, or Greek root will bring students in vocabulary development.
It occurred to me as I was writing that the meaning of pre- in prefix is obvious. It means before. However, the meaning of the suf- did not seem so obvious. In Latin words the last consonant of the prefix often changes to match the root. This is the source of most of the double consonants after the first syllable. The the prefix suf- is a variation of sub-. Just as subzero means below zero, "subfix" means below or after the word.
Since the sound /b/ followed by /f/ is difficult to pronounce, the /b/ morphs to /f/ for both spelling and pronunciation.
For more information on the prefix sub- click on the link.