from web site
Every five minutes, a perl script contacts the front page of Runescape and scrapes the displayed number of online players. agility training This is the total number of players in both versions of the game.
A second request scrapes the number of online OSRS players. The difference between the OSRS and total players is the number of EOC players
The data is stored in an electronic database that can be retrieved later for analysis and retrieval.
These numbers don't include Darkscape. Since there wasn't a huge uptick in total population when Darkscape was released, I know that its numbers are not included on the RS home page. If Jagex ever starts displaying the total player count, Darkscapes population may be included.
Other modes in the game, such ironman and deadman, will be included in totals as they aren't standalone versions. They will be lumped in with the game version they are availiable in.