compare and find differences of 2 huge text files (50 gb)

I want to find the differences between two text files (more than 50 GB) each.

I try diff but, I got memory exahusted problem.

I want such tool that give me the same result as diff.

I am using Windows7. My code is in PHP. I was calling diff from my php as:

shell_exec("C:\cygwin64\bin\bash.exe --login -c 'diff $text_files_path/$OldDatabaseFile.txt $text_files_path/$NewDatabaseFile.txt >  $text_files_path/TempDiff_$OldDatabaseFile$NewDatabaseFile.txt 2>&1'");

Someone told me about rdiff that generates signature and delta but, I did not test it because I do not know how to begin. From where can I install it? and from where can I run it? From windows cmd or cygwin cmd?

Please, I need a quick help. I have a deadline to finish this job. Any support is highly appreciated. Thanks a lot.