hi,
i am a new user on linux actually i want to know deffernce between .
/dev/tty(instances of tty),/dev/pts(instances of pts) and xterm.
what type of driver tty is and is /dev/pts also device file.

thanking you.

Put simply: tty = hardwired terminal on a serial connection. pts (a/k/a pty) is a pseudo-tty to emulate terminals on network connections.

xterm =
a) A terminal "type" definition modeled on vt100 (another type) and optimized for use with the next item.
b) An X utility that emulates a terminal - specifically emulates the DEC vt100 terminal.

Typing the following should give you a disgusting level of detail:
man terminfo
man xterm

Also:
man X
gives you some more details of settings available in X applications that may not be spelled out in xterm).
man stty
gives you some detail of other settings you can see and adjust for terminal sessions.