The subject of system performance measurement and evaluation has undergone as many generations of changes as the systems themselves. The problem of what to measure and evaluate is complicated by the fact that computing and communications, having become technically similar (digital), will undergo further fusion. Because the technologies are merging, a comparision of their respective origins is instructive. Communications and computing do not share a common history. Communications performance evalution began as a turn-of-the-century issue. Important performance attributes of voice communications systems were accessability and reliability. The general public and communications system analysts always viewed the voice communications systems as a bundled service, with little emphasis on the characteristics of its individual components. Performance was "engineered" into communications systems for given workload capacity levels (traffic). A reliable service offering evolved over two decades (1920's and 1930's) and was expanded to include data as well as voice communications. The voice network used primarily analog transmission techniques, because voice traffic grew far more rapidly than data. Pulse code modulation (PCM) techniques, employing digital transmission, reversed the trend of analog circuitry. In the future, communications transmission, switching, and integrated services networks (voice, data, facsimile, picture) will be implemented exclusively with digital techniques.