A modular synthesizer format which falls into the "small format" category. Originally derived from various standards for industrial and lab instrumentation which use the same name (and not to be confusedor with the line of low-cost mixers marketed by Behringer under this name), this Eurorack format calls for modules of 128.5mm (slightly over 5") height. Horizontal width is measured in "horizontal pitch", where 1 HP = 5.08mm (exactly 0.2"). 3.5mm mono phone jacks are used for interconnection.
The Eurorack format calls for ±12V power (most other current formats use ±15V), in addition +5V is required by some modules. Unfortunately, the orientation of the power connections are not well standardized; the format uses ribbon cables for power and a two-row ribbon cable connector containing either 10 or 16 pins. A "red stripe" on the ribbon indicates -12V. The 16-pin connector uses the extra pins to distribute +5V, control voltage and gate signals from a keyboard to the modules via a common case connection.