... The usage of catalogs is extremely important for efficiently observing with up-to-date instrumentation. In the work described in this paper, GSC sources are cross-correlated with entries in the PPM catalog, and used as an input to the control software of the Galileo Telescope (TNG). ... Maintaining the catalog on-line requires either two dedicated CD-ROM drives (or a jukebox), or over 1GB of hard disk space. ... We have created a compressed version of the GSC, called ZGSC (Smirnov & Malkov 1997a). ...