 Trains 1-42~1-63 were built from 1986 to 1989 with long, rectangular-windowed doors while trains 1-64~1-73 were built from 1991 to 1992 with short, square-windowed doors.However, many cars with rectangular-windowed doors have been refitted with 1st batch trains' doors; car 1162 was the last car with rectangular-windowed doors until its retirement in July 2016.The cars were nicknamed the "middle rheostat" cars ("중저항").