The use of modern system area networking technologies [9,3] to construct tightly integrated clusters of workstations exposes two weaknesses of current operating systems. First, the low latency of current networks is often hidden from the application due to the high cost of interrupt handling. Second, network event handling during high load may result in serious performance degradation because all processor time is used for network event handling resulting in application starvation. This paper concerns the problems related to providing efficient and stable network event handling for clusters of workstations and network servers. By stable we mean that the throughput and response time of the system does not suffer when the workload offered to the system is increased beyond the maximum capacity of the system.