(A Geek indicates a computer port.) Today it's easy connecting devices by using USB; older computers use 2 types of ports, parallel & this one
[DOC] [TLE] Serial Programming/Complete Wikibook - Wikibooks, open books for ... [PAR] 2.2.1 Straight Serial Connections; 2.2.2 Null Modems; 2.2.3 Loopback .... 6.2.6 
Handling multiple Ports in one Application; 6.2.7 Modem Control .... that transmit 
serial data over fiber optic lines, wireless transmitters, USB devices, and .....