Around 2003, the Atari 2600 vcs.h file changed greatly, in ways that make it somewhat incompatible with the older vcs.h. For instance, Thomas Jentzsch's River Raid commented source no longer assembles correctly with the new vcs.h. If you need it, there's a copy of the old vcs.h from around 2000 included in the dasm package as: /usr/share/dasm/machines/atari2600/vcs.h.old New projects should use the new vcs.h; the old one exists only for backwards compatibility with old sources.