Linux kernel fbdev
abstraction (a.k.a. Linux framebuffer), that is used by Ubuntu for most video adapters.
In Linux kernel, fbdev
is a graphic abstraction layer for accessing video (graphic) hardware in a unified way. Different video adapters needs different drivers, that may be loaded as kernel modules. Supports both text (emulated) and graphic modes.
Links:
https://help.ubuntu.com/community/ConsoleFramebuffer
http://tldp.org/HOWTO/Framebuffer-HOWTO/