In the Department of Radiology of the University of Graz a PACS which includes CT-scanners as modalities was installed. Parts (communication and archiving) of this PACS are used in routine work. Summarizing our experiences from routine work we discuss a minimal set of software requirements that a PACS must meet to allow a fast and non-problematic operation concerning communication and archiving. Most of the functionality of the PACS is provided by software processes which are running automatically in the background. These processes convert images into the ACR-Nema format, submit data in the image database and so on. If a process does not work correctly or crashes, it may happen that examinations are only partially or even not archived. If the user recognises a malfunction too late the troubles spread over the whole system and great time delays or loss of data may occur. Examples of such malfunctions are software crashes, interruptions of the connection between 2 processes or a hardware crash. A PACS that is used in routine work should conform to a set of requirements like autonomous supervising of the single processes, automatical elimination of malfunctions, communication with the user and others. Then the PACS will operate without problems and safely. An intelligent process-structure which conforms to these requirements will be discussed.