It was an unfortunate choice because \ is one of the 12 characters that vary between country versions of ISO 646 (of which ASCII was the US profile). This was w

It was an unfortunate choice because \ is one of the 12 characters that vary between country versions of ISO 646 (of which ASCII was the US profile). This was why Japanese MS-DOS used ¥ instead of \ for the directory separator: it occupied the same code point in the Japanese profile of ISO 646 that \ did in ASCII, and Shift-JIS encoded that as a single byte with the high bit clear. The complete list of the 12 was: # $ @ [ ] \ ^ ` { } | ~. Notice that / is safe. They avoided the problem for all the Western languages by inventing their own 8-bit code (this was before the ISO 8859 standards) and always using ASCII in the lower half.