Imodoka nyinshi zigezweho zifite feri kumuziga uko ari enye.Feri irashobora kuba ubwoko bwa disiki cyangwa ubwoko bwingoma. Feri yimbere igira uruhare runini muguhagarika imodoka kuruta iyinyuma, kuko feri itera uburemere bwimodoka imbere kumuziga wimbere.Benshi imodoka rero zifite feri ya disiki isanzwe ikora neza, imbere na feri yingoma inyuma.Mu gihe sisitemu zose zo gufata feri zikoreshwa kumodoka zimwe zihenze cyangwa zikora cyane, hamwe na sisitemu zose zingoma kumodoka zimwe zishaje cyangwa nto.