In this paper we briefly describe the operation of PACS(1), equipped with a central relational data base, which correlates patient identification data with the location where the related images can be found. A performance model of this PACS(1) with response times is presented in this paper. PACS(1) has also been built using as much as possible, standard software and standard protocols, to keep the development costs down. From the standards used we mention: TCP/IP, SQL, X Windows and FTP. The recent development of powerful workstations has now made it possible to eliminate the image servers in PACS(1) and integrate the functions of the image servers into the display stations. This rather simple and elegant design, called PACS(2), is presented in this paper together with a performance model. Although the development of PACS(2) has not yet been completed, we found that the presently available high power workstations are still somewhat too slow to execute, with the required response times, simultaneously the high speed communication functions and the display functions. Special purpose hardware, to implement the TCP/IP protocol functions, is introduced in the display workstation in order to reduce its workload and improve the response times.