Editing Modular synthesizer (section)

===Form factors===
Many early synthesizer modules had height in integer inches: 11" (e.g., Roland 700), 10" (e.g.,  Wavemakers), 9" (e.g., Aries), 8" (e.g., ARP 2500), 7" (e.g., Polyfusion, Buchla, Serge), 6" (e.g., [[E-mu Systems|E-mu]]) and width in 1/4" inch multiples. More recently it has become more popular to follow the standard 19" [[rack unit]] system: 6U (Wiard), 5U (8.75" e.g., Moog/Modcan), 4U (e.g., Serge), 3U ([[Eurorack]]).

Two 3U unit standards, in particular, are notable: Frac Rack (e.g., PAiA), which uses the entire 3U for the front panel, and Eurorack (e.g., Doepfer) which has a 2&nbsp;mm horizontal lip that the front panels are seated between. Further minor variations exist where European or Japanese manufacturers round a U measurement up or down to some closer convenient metric equivalent; for example, the common 5U modules are exactly {{convert|8.75|in|mm|sigfig=5}}, but non-American manufacturers may prefer 220 or 230&nbsp;mm.