/dev/cua* and /dev/ttyS*

[Richard Sharman <rsharman@magmacom.com>]

There have been various mailings here along the lines of
/dev/cua* names are deprepcated in favour of /dev/ttyS*.

I was just wondering why the change (and when).  I thought it used to
be that ttyS* was dial-in and cua* was dial-out (or possibly
vice-versa).

I looked in /usr/src/linux/Documentation,  and the only reference
I saw was in devices.txt which stated:

  4 char	TTY devices
...
		 64 = /dev/ttyS0	First serial port
		      ...
		127 = /dev/ttyS63	64th serial port

  5 char	Alternate TTY devices
...
		 64 = /dev/cua0		Callout device corresponding to ttyS0
		      ...
		127 = /dev/cua63	Callout device corresponding to ttyS63


I was just wondering,  what exactly has changed,  and why?

Richard