The CDC 6000 series computer is composed of four main functional devices: the central memory, one or two high-speed central processors, seven to ten peripheral processors (Peripheral Processing Unit, or PPU), and a display console. The four computer types differ primarily in the number of and kind of central processor. It had a distributed architecture and was a reduced instruction set (RISC) machine many years before such a term was invented.
The cars have stainless steel bodies and cab ends based on the 211 series/213 series design. The doors immediately behind the driving cabs are single-leaf instead of the pairs of doors used at other locations.
The 6000 series was a series of Chicago "L" car built between 1950 and 1959 by the St. Louis Car Company. 720 cars were built. The last of 6000-series cars were retired on December 4, 1992. These cars were in service for 42 years.
In 1947-1948 the CTA received four three car articulated trainsets, 5001-5004, to test PCC technology in rapid transit use. Two sets of cars were built by Pullman, two by St. Louis Car, with equipment supplied by competing suppliers, in order to test them directly against each other. The 6000 series was designed with knowledge from the 5000 series.
5000 series bodies had a curved profile previously used by North Shore Line and then Chicago, Aurora & Elgin cars which operated on the L. The floor width was the 8ft 8in (2.64m) needed for platform clearance, then above the sides curved outward, so the car was wider at seat level. This profile was used, 6000 series cars were 8in (20cm) wider at the seats than the floor. Blinker doors which fold and open inward were also successful and were used in the 6000 series.