Overview
The VGA is divided into roughly 5 sections: a set of general
purpose registers for global or external control; a set of
sequencer registers that control the clocking or sequencing of
pixels to the VGA monitor; the CRT controller registers which
which set up the fundamental display resolutions and the timing
of vertical and horizontal retrace and blanking; the graphics
controller registers which control the special features of
the graphics ALU for modifying pixels in the memory; and the
attribute controller registers which control the palette and
handle part of the panning features.
There is a special extension to the attribute controller
section in the VGA which provides for the color register
extensions to the EGA palette.
[I have much more to add here, just haven't had time, yet.]