Controller keyboards were designed to aid the musician utilising MIDI to control several other keyboards or sound modules in a live or recording environment. MIDI instruments are able to transfer data amongst each other using a feature called system exclusive data (sysex data). Each MIDI instrument can also be configured to be a master or slave unit and may allow control parameters such as programme changes or tempo to occur.
Controller keyboards are designed without any on-board sounds, but with full MIDI capability and sufficient memory capacity to control several other keyboards or sound modules simultaneously. Sound modules are effectively the electronic components, software and sound patches that make up a normal electronic keyboard, but without the actual musical keyboard. They are often in 19" rack mount chassis format and a whole bank of them can be controlled by a single MIDI controller keyboard.
