For instance, under Linux the special files for SCSI disk drives should have a major number of 8, while the major number for an IDE disk drive's special file would be 3. Minor Number A file's minor number is similar in concept to the major number, but conveys different information to the device driver. In the case of disk drives, this information can consist of a unit identifier. Should the minor number change, RPM will detect it. If the file in question is really a symbolic link, the text string containing the name of the linked-to file is checked.
Most operating systems keep track of the date and time that a file was last modified.
RPM uses this to its advantage by keeping modification times in its database. Actually, the price is fairly low. For a completely RPM-based Linux distribution, it would be unusual to have a database over 5MB in size.