Bitcoin is a protocol actually, that store numbers in a peer to peer ledger, what you do is change the values on the ledger, and the encryption is only to ensure the transaction was not a forgery.
Right now the protocol supports as the smallest one the "satoshi", but a "satoshi" is too small, so people for day to day use "BTC".
0.00000001 of a BTC is a satoshi.
But if Bitcoin really gets used in the mainstream, BTC might be valued in the millions, thus the protocol can be more or less easily changed to use a unit smaller than the satoshi.
Bitcoin is a protocol actually, that store numbers in a peer to peer ledger, what you do is change the values on the ledger, and the encryption is only to ensure the transaction was not a forgery.
Right now the protocol supports as the smallest one the "satoshi", but a "satoshi" is too small, so people for day to day use "BTC".
0.00000001 of a BTC is a satoshi.
But if Bitcoin really gets used in the mainstream, BTC might be valued in the millions, thus the protocol can be more or less easily changed to use a unit smaller than the satoshi.