fc | Microsoft Learn

When comparing ASCII files, fc uses an internal buffer (large enough to hold 100 lines) as storage. If the files are larger than the buffer, fc compares what it can load into the buffer. If fc doesn’t find a match in the loaded portions of the files, it stops and displays the following message: Resynch failed. Files are too different.

https://learn.microsoft.com/en-us/windows-server/administration/windows-commands/fc