A complete sample that has been given number 123 should have two attached data files (at minimum): 123.cif and 123.crt. You are free to attach as many data files to each sample as you wish – some people include gif images, ort files for ORTEP renderings, pdb files, and so forth. The crt file in particular has special significance: it contains coordinate data about the unit cell observed in this sample and is required for JaMM (a Java applet for molecular visualization) to function. You may include multiple crt files depicting alternate views of the sample for users to switch between if you wish; in such a case the crt file named 123.crt would describe the default view.