attrib [options] [[d:][path]file]
+r | -r Sets the read-only attribute. -r clears it. +a | -a Sets the archive attribute. -a clears it. +s | -s Sets the system attribute. -s clears it. +h | -h Sets the hidden attribute. -h clears it. /s Acts on subdirectories, too.
If no file is specified, then the attributes for all files in the current directory are changed (or simply displayed if none of the above specifiers are used.)
The archive attribute is set when a file is modified. Backup utilities can clear the attribute to indicate that the file has been backed up.