One-way disc is all one gang, discer has more, shorter ,gangs. Discers were very popular across the Canadian prairies until air seeders came along, still some smaller farms using them. Big operators had multiple units, like 5 , 15 or 18 foot setups behind a Versatile or some such 4WD. We built tandem hitches for several guys, and one for ourselves. Apparently the only other place they were common was Tanzania, since the Canadian govt sent prairie farmers there as advisors to get their economy going. One thing I miss is the smell of freshly-turned soil. Strange how no other implement makes the earth smell that sweet!