Maighstir: Why would the operating system arbitrarily limit the size of files just because their file names happen to end with ".txt"? Shouldn't that be the job of the application producing said files?
CharlesGrey: I seem to recall there was a limit, but maybe that was on older Windows versions. Probably related to the amount of text it could actually display and load into memory without having some kind of spasm. 50GB of text is a ridiculous amount, in any case. My entire collection of e-books and writing has a size of less than 50MB. :D
I recall Notepad having had a limit on how much data it could handle at a time. But, again, that's a limit of the application, not the OS or FS, to the file system, it's just data.