The Class 423 EMU is a light-weight articulated electric railcar for S-Bahn commuter networks in Germany. The train has similar dimensions to its predecessor, the Class 420 EMU, but is significantly lighter and has one large passenger compartment, while that of the 420 is divided into three parts. The 423 additionally has six doors in each carriage (three on each side), which is down from eight on the 420 (four on each side). They are numbered from 423 001 to 423 462. Both Munich and Frankfurt have ordered Class 423s for their S-Bahn systems since 1998; they were delivered between 1999 and 2004.

Source: https://en.wikipedia.org/wiki/DBAG_Class_423