The IBM RISC System/6000 Keyboard was a variant of the Enhanced Keyboard featuring an integrated speaker on the bottom side of the casing. The speaker is believed to act as an audible cue when keys are pressed, similar to the purpose of solenoids in some earlier Beam spring and Model F keyboards. The speaker connects via a usually unused pin in the PS/2 plug, thus the speaker cannot be used on other systems without intercepting the signal with an additional separate circuit.