Wireless high-speed data systems based on 1xEV-DO have recently been deployed commercially and in field trials. In this paper, the emphasis is placed on the validation of the simulated forward link system-level performance through comparison with field data. High spectrum efficiency observed both in simulations and in the field is explained by the salient features of 1xEV-DO that make it suitable for data communications in a cellular mobile environment. These features include, among others, the long-range channel estimation and rate prediction, incremental redundancy hybrid automatic request control (ARQ), turbo coding, and scheduling that exploits multi-user diversity in a fast fading environment. The paper also addresses the reverse link performance and the practical system constraints imposed by the signaling overhead necessary to support high throughput on the forward link.