Jed Margolin, Atari engineer, wrote the ultimate papers on how the Atari vector games worked. These two pieces are excellent reading when you have the time:

The Secret Life of XY Monitors : http://jedmargolin.com/xy/xymons.htm

The Secret Life of Vector Generators : http://jedmargolin.com/vgens/vgmenu.htm

The first covers how the tube worked, the second covers how the Atari systems generated the graphics to show on-screen.