4chon menus

I don't get it.

[a / b / c / d / e / f / g / gif / h / hr / k / m / o / p / r / s / t / u / v / w / wg] [i / ic] [cm / y] [r9k] [an / cgl / ck / co / fa / fit / hc / jp / mu / n / po / sp / tg / toy / trv / tv / x] [rs] [status]

How are these grouped?

[a / b / c / d / e / f / g / gif / h / hr / k / m / o / p / r / s / t / u / v / w / wg]
[i / ic]
[cm / y]
[r9k]
[an / cgl / ck / co / fa / fit / hc / jp / mu / n / po / sp / tg / toy / trv / tv / x]
[rs]
[status]

It's not by server.

>>3
When was /co/ first introduced on 4chan?