what's the differrence among un-,in,non,dis?
reliable ---> unreliable (not reliable)
conclusive ---> inconclusive (not conclusive)
ferrous ---> nonferrous (not an iron metal)
satisfied ---> dissatisfied (not satisfied)
There are a few more "not" prefixes that you have not mentioned here such as :
a, theist ---> atheist (not a believer in god)
im, possible ---> impossible (not possible)
il, legal ---> illegal (not legal)
ir, responsible ---> irresponsible (not responsible)
There is no difference in meaning in the prefixes but you cannot use them on different words.
impossible is correct
nonpossible, unpossible, apossible, inpossible, dispossible, ilpossible and irpossible are all incorrect. (not correct)
There are basically no rules about which "not" belongs to which word unfortunately. To a native English speakers ear the correct one sounds right to us...but that doesn't help you I'm afraid. You basically must memorize the correct combinations.
I hope this helps.