I have learnt that all data transmission is analog. Is there any mediums that could transmit bits digitally?
HDMI interface is one example of being able to tranmit high-speed digital data. It works using an encoding technique called TMDS (Transition Minimized Differential Signaling) which you can read more about here
Also, HDMI can only be used with older analog-only devices (using connections such as VGA, etc.) by means of a digital-to-analog converter or AV receiver, as the interface does not carry any analog signals from Wikipedia