a-
8.3 filenames are limited to at most eight characters (after any directory specifier), followed optionally by a filename extension consisting of a period . and at most three further characters. For systems that only support 8.3 filenames, excess characters are ignored. If a file name has no extension, a trailing . has no significance (that is, myfile and myfile. are equivalent). Furthermore, file and directory names are uppercase in this system, even though systems that use the 8.3 standard are usually case-insensitive (making CamelCap.tpu equivalent to the name CAMELCAP.TPU).
https://en.wikipedia.org/wiki/8.3_filename