> I don't know how a GUI could be created without being built on something at a lower level
Which simply makes my point that being CLI-centric has limited your imagination. In fact the original Mac had a UI built directly on top of the system libraries. On startup it displayed an icon and played a chime (which was its hardware self-test result). Insofar as there was a "CLI" it ran UNDER the GUI. (There is something lower level going on that the GUI, but it's not a terminal.)
Even on a primitive command line machine, there's stuff going on below the level of the command line. In Linux you're running a shell, which is actually not part of the kernel. The fact that the kernel can spew text onto the screen during startup is merely an artifact of what's easy to do using the computer's BIOS or equivalent thereof.
Which simply makes my point that being CLI-centric has limited your imagination. In fact the original Mac had a UI built directly on top of the system libraries. On startup it displayed an icon and played a chime (which was its hardware self-test result). Insofar as there was a "CLI" it ran UNDER the GUI. (There is something lower level going on that the GUI, but it's not a terminal.)
Even on a primitive command line machine, there's stuff going on below the level of the command line. In Linux you're running a shell, which is actually not part of the kernel. The fact that the kernel can spew text onto the screen during startup is merely an artifact of what's easy to do using the computer's BIOS or equivalent thereof.