Abstract: SCI（scalable coherent interface） is a high speed interconnect standard approved by IEEE in 1992. It provides a high performance, cost effective, and scalable solution to the interconnection of cluster systems. In order to fully utilize the high raw bandwidth of SCI, a more efficient input queue allocation protocol, Called intelligent A/B aging protocol is proposed. The implementation and performance evaluation of the intelligent A/B aging protocol is also given. It notably increases the bandwidth utilization and shortens the average service delay of send packets. The analysis shows that thd intelligent A/B aging protocol improves performance more significantly as the workload of the system increases.