As already mentioned EXSAS makes full usage of the MIDAS table and image file structures. Nevertheless there is a distinct and very important difference between a file created by a MIDAS command and one created by an EXSAS application task: files created by EXSAS possess an additional header section used to transfer accompanying information (instrument setup, observation parameters etc.) between EXSAS tasks. MIDAS commands do not access this EXSAS header. Therefore files created or changed by MIDAS commands can generally not be treated correctly any more by subsequent EXSAS commands. Although usually this is not a problem, the user should always keep this difference in mind.
The EXSAS header section coming along with each EXSAS table or image contains an EXSAS file type entry. This entry is used to uniquely identify different types of file contents and/or structures. The user can therefore usually name data files freely. Two of the most important file types will be shortly discussed in the following.