A+: File attributes and Extensions
ATTRIB, a comand-line application, shows you details about the metadata of a file; whether it can be changed (R), if it has been archived (A), if it is a System file (S) and if it is Hidden (H) from appearing in Windows Explorer and with DIR. + Sets an attibute, and - clears it; /S alters files in the current directory and subdirectories beneath it, and /D modifies folders as well as files.
The Recovery Console in XP and 2000 doesn't have the /S or /D options but instead offers +C to compress a file and -C to extract a file from compression.
Windows Explorer allows you to right-click on a file, select Properties from the Context Menu which appears, and then see and change the attributes in lieu of using ATTRIB from the command line.
Extensions are the part of the file name following the last period. Files with the extensions .BAT, .CMD, .COM and .EXE can be run from the command line prompt, and are considered Executable; other files in the system are consider Data files, even if they're part of a program and the program won't run without them.