Recently, the scheme of parallel downloading (PD) has been adopted by a number of Internet file downloading applications. With the wide deployment of content distribution networks and peer-to-peer networks, PD is expected to be more commonly used for file distribution. There have been experiments showing that PD results in higher aggregated downloading throughput and therefore shorter downloading time experienced by clients. However, these experimental studies focused on the performance experienced by a particular user and did not consider the impact of PD on the network when it is largely deployed. In this paper we present our efforts toward an in-depth understanding of large-scale deployment of PD through simulation and analysis. Our results suggest that while PD may achieve a shorter downloading time, its impact on the network and server is signi.cant. Our analysis is also used for network dimensioning and content distribution service provisioning. We show that with proper admission control and dimensioning, single-server downloading can perform just as well as PD, without the complexity and overhead incurred by PD.