FC is the name of a DOS utility program, File Compare. The file name of the program is FC.EXE.

My Google searches show it to be part of (probably IBM's) DOS 7, but if memory serves me correctly it was part of MSDOS versions as early as 4.0 or 5.0 . I remember being very happy to see this program bundled with DOS because file comparison is a very useful utility to a DOS batch file programmer, and there were few similar utilities available for the DOS platform.

Here are FC's options, which give an impression of its capabilities:

Performs a binary comparison
Compares files as ASCII
Set the number of lines for the internal line buffer
The number of consecutive lines that must match before the files are declared resynchronized
Displays the line numbers on an ASCII comparison
Abbreviates the output of an ASCII comparison
Disregards the case of letters
Does not expand tabs to spaces
Compresses tabs and multiple spaces to a single space for the comparison
This list shows that FC can be used for binary and ASCII comparisons, and that it can be told how to deal with some of the variations in ASCII text that may lead to negligible differences. It also shows that FC uses a relatively simple windowing/re-synchronizing algorithm almost universally used in file comparison programs. Though sufficient in most cases, FC does not yield minimal difference sets like the Optimal difference algorithm.