There are three types of mowers; sickle bar mowers, disc mowers, and drum mower. Sickle bar mowers use a reciprocating knife to cut the grass and typically use a reel to fold the grass over the knife. Disc mowers have a number of hubs across the cutting width, each hub having a small (18”) rotating disc with knives. Drum mowers use two or three large plates (called the drums, about 36” across) which ride over the ground as they are spinning. A sickle bar mower’s main advantage over disc mower and drum mower is the reduced horsepower requirements. Its disadvantage is the extra maintenance required due to the high number of moving parts and wear items. Disc mowers were historically considered an “all the eggs in one basket” kind of mower because all the mower hubs were one large gearbox. If one blade hit something and a gear tooth broke the whole gearbox would suffer a catastrophic failure and there would be nothing worth fixing. If anything broke, everything broke. Drum mowers prevented this by having typically two belt-driven drums compared to 6 or more gear-driven hubs. Modern disc mowers use isolated gearboxes and if one fails it can be swapped out without rebuilding the entire machine.