Linux uses run levels in which it starts programs as the computer boots.
0 --> when the computer shuts down
s or 1 --> when the computer boots
2,3,4,5 --> different run levels (you can see which programs boot in each in /etc/rc2.d/,/etc/rc3.d/, /etc/rc4.d/ etc...
6 --> a reboot
if you wanted to jump straight to a run level you can use the command telinit 3, telinit5 etc.
Note that apparently distrobutions can choose to have programs run at different run levels. I cannot remember the man page that I read this in. sorry.