The head may or may not alter its internal state and may or may not overwrite a symbol on the tape.
Created as a solution to the Entscheidungsproblem, this theoretical construct consists of a head and a tape. The head may or may not alter its internal state and may or may not overwrite a symbol on the tape. Depending on the input, the head performs an operation such as moving to the right or left or halting the tape.  FTP name this device, the basis for modern computers.
Created as a solution to the Entscheidungsproblem, this theoretical construct consists of a head and a tape.
Turing machine