This paper advocates local area networks using the Asynchronous Transfer Mode where data is carried in the payloads of fixed size cells. We describe the design and performance of a simple ATM host interface for a RISC workstation together with the MSNA protocol architecture. A feature of the MSNA architecture is that it can provide ATM virtual circuits directly to applications by demultiplexing to a degree normally associated with the transport layer of a protocol stack. We discuss implementations of the ATM adaptation layer of varying complexity and discuss the appropriate place for the adaptation layer to be terminated in a multi-media workstation.