What is the relationship between framebuffer, VT, and tty?
- Correct tty and pty are terminals. but there is small difference. pty is pseudo terminals. open a terminal type tty will return pts terminal. tty are generally physical if you have used embedded linux you can redirect linux console to different tty which are uart terminals. if you use a 9 pin uart cable. then you can use ttyX.
vcs are differant screens were used pre X-Server erra. or now in server where X server( or even Wayland Server) is not installed. in run level 3 and 5. to try use CTRL + ALT + F3 to access /dev/vc3. you can echo and cat simmilarly.
frame buffer is part of Graphic subsystem its not supposed to be used with cat. It is matrix. its abstraction over any screen connected. to be used by graphical drivers and applications.