About the RS-232 serial port
The ZX Interface 1 features an RS-232 serial port which allows the Spectrum to be connected to other computers and peripherals, such as a serial printer.
Spectaculator can either redirect serial input and output to/from files or use a real serial (COM) port on your computer. This can be useful as it allows Spectaculator to be connected to a real Spectrum by attaching a suitable cable between the real Spectrum's Interface 1 and a free serial (COM) port on your computer.
For further information, see the ZX Interface 1 and ZX Microdrive manual, available here.
Tip
Normally, you want to configure the same COM port for both input and output. However, sometimes it can be useful to say, configure serial input to a COM port and serial output to a file. This way it's possible to receive data from a real Spectrum and write it to a local file on your computer.
Details on building your own RS-232 cable to connect to a real Spectrum can be found here.