IOS family naming

Hi List, Anyone recalls ever seeing the IOS naming convention document. In particular I'm interested in differences between families and trains. This is all I found: http://www.cisco.com/warp/public/620/1.html#topic1 But im looking for something a bit more recent maybe? Can figure out differences between say SG, SGA, EW and EWA. A link to the cipher would certainly help. ----- Andrey Gordon [andrey.gordon@gmail.com]