Bass pedals
Bass pedals are an electronic musical instrument. Analogous to the keyboard on keyboard instrument, they consist of a set of pedals for each semitone in the octave, laid out in the traditional pattern of black and white notes. Most pedalboards contain either one, two, or two-and-a-half octaves' worth of pedals. The pedals are played with the feet, and are usually set to play notes in the deep bass register.
These pedals were made by different companies, with slightly different sounds and features, but all based upon the same idea: the traditional organ pedal set has a standard piano keyboard, but made larger and longer to accommodate the feet. Typically, these pedal sets are only an octave or so long, which limits the player. They are almost always tuned to the low bass octave, although modern MIDI bass pedals allow any octave to be controlled. Electronic bass pedals are based on the pedal boards which formed part of pipe organs. In the early 20th century, electromechanical organs such as the Hammond organ and Farfisa were developed, and these too usually included bass pedals. By the late 1960s, some manufacturers began to build stand-alone electronic bass pedal units. These were intended to be much more portable than large organs, and could be used under a separate keyboard or keyboards.
Several progressive rock groups incorporated bass pedals into their instrumentation, often played by the group's bass guitarist whilst in a standing position, meaning that they could only use one foot at a time to play, rather than play sitting down with both feet as organists traditionally had.
Fender models
Fender bass pedals were a set of organ-style pedals from the 1960s, that were a portable octave of pedals that generated low bass tones. They could be set for immediate attack and release (as an organ-type tone) or a 'string bass' sound that decayed away, instead of sustaining.
Moog Taurus
The Moog pedals were similar to the others, only with a more powerful, flexible analog synthesizer attached. The pedals created a huge, heavy sound if needed. The first series was not assigned a number although these pedals are now commonly called the 'Taurus 1', because Moog issued a second set called 'Taurus 2'. Many musicians feel the 'Taurus 1' has better tone, while the 'Taurus 2' has more features.
Usage
Yes and Genesis were known to use various model bass pedals.
John Paul Jones of Led Zeppelin was a heavy user of bass pedals. At one point in 1977, Jones was touring with four sets of pedals onstage, so that he could play bass with his feet no matter which instrument he was playing. Jones used Fender pedals for the only the early Led Zeppelin tours. Jones' main pedal set was a custom-built unit, made by Bill Dunn of London. Jones had Dunn build pedals that were very similar in tone to a Hammond bass pedal tone, but more mellow. His control box for the Dunn pedals would sit on top of the Fender Rhodes piano, and he was often seen adjusting the volume of the pedals during concerts. The Dunn control box has been a very recognizable part of Jones' onstage rig. For the 1975 Physical Graffiti tour and after, Jones would also use Moog Taurus pedals, and these were often used while Jones played acoustic guitar during the acoustic sets.