The series 120 and 121 comprise a total of 57 four-car multiple units for fast regional transport. The special feature is that the trains can be re-gauged between the standard gauge and the Iberian broad gauge within a minute. On the new standard-gauge lines with 25 kV AC they reach 250 km/h with an output of 4,000 kW and on the broad-gauge lines under 3,000 V DC the top speed is limited to 220 km/h with 2,700 kW. The 29 trains of the series 121 differ from the series 120 in that there is no first class and no cafeteria. 