You may also easily achieve a 4 fire button config by using both directional pads (one for each thumb yet the cable would be a nuisance) or a fixed Joystick (right hand, directions) + a paddle (left hand, fires).
==PC controllers==
Good old controllers for IBM PC & Compatibles weren't always USB, as it didn't really existed in the early 90s.
Many of them used a DA-15 connector, the same as the analog port on Amstrad Plus, wich was often pluged into the soundcard (Sound Blaster card was in fact game card...).
Those joystick weren't always analog too and many can still be found in your old cave awaiting a new life.
DA-15/DE-9 adaptators can also still be found.
More research concerning those's Pin-out schematics would be quite interesting.
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Image:Genius power station.jpg|The Epic Awesomeness of the dreadfull PowerStation by Genius.
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More pics to come.