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Vertically it occupies the same space as a 3U (3 rack units) enclosure in the 19" rack standard (the most common rack standard for most kinds of equipment). Horizontally units typically called HP (Horizontal Pitch) are used, where each HP is equivalent to "one screw hole" in the rails. 19" rack enclosures for Eurorack are available, typically containing 84HP. Each mounring-rail usually has a slit for inserting an strip of metal with screw-holes. These holes are typically 3M M3 but may in some exceptions be 2M2.5M5.
Electrically, eurorack specifies that modules receive ±12V and (optionally) +5V from a common power supply in the rack. In modern modules, 5V is rarely used. Eurorack also specifies that signals are exchanged between modules via 3.5mm mono jack cables. These can be audio signals, control voltages, trigger, gate or clock signals, or sometimes video signals.
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