[jcrawfordor]

Perhaps a marginally better title would be "EOF is not a character [on Unix]". There are some OS that have an explicit EOF character, but it seems to have been the less common approach historically. CP/M featured an explicit end of file marker because the file system didn't bother to handle the problem of files which were not block-aligned, so the application layer needed to detect where the actual end of the file was located (lest it read the contents of the rest of the block). This is a pretty unusual thing to do, and was definitely a hassle for developers, so CP/M descendants like MS-DOS fixed it.

[mark-r]

I think CP/M copied that convention from an even older OS but I can't remember which one.

[jcrawfordor]

CP/M was developed on TOPS-10 and copied a lot of concepts from it. I can't immediately tell whether or not this is an example, but for any given eccentricity of CP/M it's a good bet that it came from TOPS-10.

It's amusing that almost the same can be said about NT: for any given eccentricity of Windows NT it's a good bet that it came from VMS, since the two had the same principal designer.

[kevin_thibedeau]

This also afflicts the xmodem protocol.