It has been widely recognized in the past that archives containing raw or preprocessed data can only be effectively used if appropriate analysis software is commonly available. For ROSAT data the answer to that requirement is called Extended Scientific Analysis System (EXSAS) [Zimmermann et al.1992]. EXSAS has been developed by the RSDC for interactive analysis of X-ray data in general, with particular emphasis on the analysis of data from the ROSAT XRT and WFC instruments. This large collection of application software modules is embedded in the well-known astronomical image processing system ESO-MIDAS, developed, maintained and distributed by the European Southern Observatory ESO. EXSAS/MIDAS is portable and has been installed on both VMS and different UNIX operating systems. In order to guarantee computer system independence with respect to data distribution, all data input to EXSAS has to be in FITS format (Flexible Image Transport System: a data transfer standard widely accepted by the astronomical community).
EXSAS software may be requested from the RSDC by ROSAT observers having access to a MIDAS installation.