Aiming at the frequent failures in the PACS clinical applications, a continuous availability (CA) image server with triple modular redundancy (TMR) is designed and used for failover at the CPU/memory level. The TMR voter, which is included in the CA image server, is applied to detection of failures. Through UW or FW SCSI interfaces, two mirror-image disks, two RAID controllers and two DLT controllers are respectively connected to the modules in the TMR and a complete CA image server is brought into being. The CA image server will replace the potential single point of failure (SPOF) in the PACS and increases its availability rate to 99.999%. The advantages of the TMR CA image server make itself well suitable for large-scale medical image network and database applications.