This paper describes the architecture and some of the main features of the MainStreetXpress 36190 ATM core services switch. This switch has been designed from the start as a fully functional, central office class ATM switch which can be used already today to create the backbone layer for commercial ATM-based multi-service networks. Due to its modular hardware and software architecture, it provides the required flexibility with respect to interface requirements, signalling/control capabilities and service support. The architecture together with the ATM chip set specifically developed for this switch allows to extend the data throughput of the MainStreetXpress 36190 from 5 Gbit/s into the Tbit/s range by just scaling the central switch fabric. The call processing capability can be scaled well into the MBHCA range (Million Busy Hour Call Attempts) by taking advantage of the specifically developed multi-processor control platform. Full redundancy for all central hardware components and optional redundancy for interface boards and external transmission lines is provided. In combination with a comprehensive hardware/software maintenance and recovery concept based on the vast experience with the EWSD line of digital switches these capabilities provide the reliability and availability required for large ATM carrier networks. Together with the full line of MainStreetXpress components – ranging from network terminations and LAN service units via flexible access multiplexers/switches to scalable ATM multi-service switches and a variety of specific server types all controlled by a common network and service management – the MainStreetXpress 36190 provides carriers with the means to realize fully functional, cost effective ATM based multi-service platforms already today.