SFTP is a binary protocol, and the latest version is standardized in RFC 4253. All the requests of commands are already packed to binary messages and sent over to the server, which is replying with binary reply packets. In its later versions, SFTP has been extended to provide not just the download/upload operations, but some file-system operations such as symbolic link creation and file lock etc.
Both SFTP and FTPS use asymmetric algorithm as a combination (RSA, DSA), key-exchange algorithm, and symmetric algorithm (DES/3DES, AES, Twhofish etc). FTPS (or SSL/TLS protocol under FTP) uses certificates of X.509 while SFTP (SSH protocol) uses keys of SSH for authentication.