Serial
Depends, is the device serial or parallel?
A telegraph key.
serial device
Serial ports only allow one device to send and one device to receive at a time, where a parallel port can send and receive data at the same time.
Yes, a telegraph is a device for sending messages. It sends telegrams.
Neither. A computer case is just a box to hold the parts of a computer. It provides no form of communication itself.
parallel
Some key differences between a Serial and Parallel Adder are that a Serial Adder is slower, a Parallel adder is a combinational circuit and the time required for addition depends on the number of bits in a Serial, but not a Parallel. A Serial Adder is a sequential circuit while a Parallel is a combinational circuit.
multiplexer can be used as parallel to serial converter.
Usually serial. Parallel is almost completely gone, and serial is getting replaced by USB.
telegraph
A universal asynchronous receiver/transmitter, abbreviated UART ( /ˈjuːɑrt/), is a type of "asynchronous receiver/transmitter", a piece of computer hardware that translates data between parallel and serial forms