Traction elevator machine rooms are located just above the elevator shaft served by that equipment. In the case of a geared drive system, machine rooms are typically found next to the elevator hoistway or at the bottom of the shaft. Especially in older installations in high-rise buildings where space is limited, the machine room is often split into two levels to accommodate the traction equipment, motor-generator (MG) sets, and relay control devices. Typically, upgrading to a solid-state controller and variable frequency drive (instead of the MG sets) can free up this space for other uses.