Arts and alsa are totally different things.
Alsa is the sound DRIVER. Arts is a sound SERVER (like Esd).
http://www.alsa-project.org/ http://www.arts-project.org/
Drivers live in the kernel. OSS was alsa's predecessor. (not strictly true, alsa does require 1 or 2 userland programs, but its a non-issue here)
If you don't beleive me, do lsmod.
if you get ones like snd-card-**** then its alsa. OSS just had normal module names.
Sound servers are there to try and make the problems associated with file-locking the device nodes a thing of the past, but unfortunatley they tie the node up themselves. Arts is better than some in that you can configure it to give up the handle if there's no sound through it in a few seconds.
If you still don't get it, follow those links.
Linear Mode
