When creating or renaming a file, you need to be aware of the file naming conventions. Filenames on SUN UNIX are significant up to 255 characters, but for portability and ease-of-use you should try to keep your filenames below thirty characters in length. Note that non-alphabetic characters such as a period ('.') can occur more than once in a filename string (unlike the MSDOS filenames that you may be familiar with). Standard file extensions are used to denote different types of files, i.e. .c for C language source, .o for object files, .a for library files, .p for pascal, .f for fortran, etc. Files should always be named as descriptively as possible to enable you to determine file contents from the name. Subdirectories should be used for organizing related files.