Early Atari home consoles had simple, direct-current controllers with nine pins in the connnector. Of those pins, seven were available for input to the hardware for games and programs.
The Atari joystick used five of those pins for 1 trigger button and a 4-directional stick.
Atari "paddles" were a pair of dials which could each input a value between 0 and 255. It used the last 2 of the available pins for this input. Two triggers paired with the dials used some of the same pins as the joystick.
This means that each of these standard Atari controllers only used part of the potential of the 9-pin port they were plugged into. A controller that took full advantage of the Atari controller port would perhaps have a four-directional joystick, one trigger, and two dials to use all of the available inputs.
Controllers have changed a lot since those days. Later game systems have used special signals for input instead of direct currents, and no longer have a number of pins directly related to the numbers of inputs available. They've gotten easier to hold and handle, added more buttons, adopted new standards, and added analog sticks, among other things, but there are foundations that have stayed true until today, and there are parallels to be drawn between these early controllers and the most modern controllers we use today.
To be continued... the D-Pad, and more and more buttons.
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