I would be very surprised to see an RS232 port on all those devices. The original RS2323 port had 25 pins, but then a newer version with only 9 pins (the rest were unused for most applications) became common. That 9-pin port can look a lot like some other ports, so maybe you are confused on some of your devices.
RS232 is simply a serial data transmission / communication port. It has never had any signals involved in video. It has been used for data exchange between computers and for connecting peripheral devices like modems and printers to computers. It also has been used to connect a remote keyboard / screen, such as a "dumb terminal", to a computer as an additional I/O device.