TCP/IP provides a total of 65,535 ports of which 1023 are considered to be well known ports.
In reality the number of ports that are used by popular network clients and services comprises an even smaller subset of the well known group of ports.
Most commonly, however, UDP is only used in special cases.
The UDP applications topic describes the two types of protocols that may be better suited to UDP than TCP: ones where speed is more important than reliability, and ones that send only short messages infrequently.
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FTP uses TCP (rather than UDP) to transfer files so is considered to be a highly reliable transport mechanism.
FTP does not encrypt data and is not considered to be a secure file transfer protocol.
Given that it is responsible for large transfers of files and UDP is unreliable, this was probably not the best idea, and TCP versions were created. A couple of the protocols in the table above use both TCP and UDP, to get the best of both worlds.
Short, simple messages can be sent with UDP, while larger files are moved with TCP.