Each page in a database has a file number and a page number that uniquely identifies its location in the database. When you restore a database, the pages keep their original file numbers and page numbers. Consequently, you must replace the restored database in the same number of files as the original. If your original database contained five data files, the new database must also have five data files. If the original database used only two data files—one for the primary file and a 48GB file as the secondary data file, for example—you must use two data files for the restore, and one of the files must be at least 48GB.
When you plan how many data files to use for your original database, remember that restoring to a smaller number of physical files than you had originally is easier than restoring to a larger number because you can place multiple logical files on one physical file, but you can't place one logical file on multiple physical files. If the original database had one 48GB file, you can't restore it to more than one file. However, if you created your original database in six 8GB files, you can restore to a 48GB physical disk by creating six files on the same disk, you can restore to two 24GB disks that each contain three files, or you can restore to three 16GB disks.