Eurorack is by far the most familiar format. The height is 128.5 mm. Widths are multiples of 1 HP = 0.2 inches = 5.08 mm. Patching jacks are 3.5 mm phone jacks.
Most other formats are physically larger than this. The MOTM format, for instance, has height 5U (8.75 inches) and minimum width 1U (1.75 inches). Patch jacks are 1/4" phone jacks.
Smaller height doesn’t mean a smaller system if there is a corresponding increase in module width. But in the Eurorack community, there is a prevalent attitude that narrower is better. Almost the first thing people want to know about a Eurorack module is, how narrow is it? At least one company specializes in modules that are the minimum feasible width of 2 HP. The smaller patching jacks facilitate making the modules smaller; so do use of small knobs, or even no knobs at all — just knurled potentiometer shafts — and close spacing of jacks, pots, and switches.
Three Eurorack modules
The obvious advantage to Eurorack is that its smaller size makes for systems that take up less space and are easier to transport.
The disadvantages are less commonly mentioned. One is that making a module narrower generally makes it harder, and therefore more expensive, to produce.
Another, in the view of some users, is that 3.5 mm patch cords are not as robust as 1/4" ones.
But the main drawback is ergonomic. If your approach to synthesis is to set up a patch and tweak it to get a sound you like, and then hit “record”, play something on a keyboard, and hit “stop”, this kind of condensed design might be fine. But for many synthesists, especially live performers, the whole point of analog synthesizers’ knob-per-function design is to let you vary the sound manually in real time. The knobs are used as performance controls. But if tiny knobs or pot shafts are crammed close together and in close proximity to patch cords, then they are hard to find, hard to grip, and hard to manipulate without bumping into other knobs.
Look Mum No Computer, a.k.a. Sam Battle, is a performer of the latter school. After trying Eurorack, Sam decided it didn’t suit his style, so he created Kosmo. Here you seem him playing the knobs on his Kosmo synth (and a couple of Korgs).
LMNC on synth, playing the knobs
That kind of performance style is not well suited to Eurorack designs.
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