This tidbit from the DOS 2.0 README.txt (section 5) is fascinating: The user manual contains some significant errors. Most of these are due to last minute

This tidbit from the DOS 2.0 README.txt (section 5) is fascinating: The user manual contains some significant errors. Most of these are due to last minute changes to achieve a greater degree of compatibility with IBM's implementation of MS-DOS (PC DOS). This includes the use of "\" instead of "/" as the path separator, and "/" instead of "-" as the switch character. For transporting of batch files across machines, Microsoft encourages the use of "\" and "/" respectively in the U.S. market. (See DOSPATCH.TXT for how you can overide this. The user guide explains how the end-user can override this in CONFIG.SYS). Also this, from the documentation for the CharOper system call (that never made it outside of MSFT?) in SYSCALL.txt: AL Function -- -------- 0 DL, on return, will contain the DOS switch character. On most systems this will default to '-'. 1 Set the switch character to the character in DL. 2 Read the device availability byte into DL. If this byte is 0, then devices must be accessed in file I/O calls by /dev/device. If this byte is non-zero, then the devices are available at every node of the directory tree (i.e. CON is the console device not the file CON). This byte is generally 0. 3 Set the device availability byte to the value in DL. It looks like we have IBM to blame for '\' and '/' as a path separator/switch character in DOS/Windows, Microsoft originally was using the Xenix '/' and '-' respectively. I knew that Microsoft used Xenix fairly heavily internally but never thought that DOS was quite so influenced by it.