[CentOS] How does Live CD find OS's?

If I boot into CentOS on my home server from a Live CD or USB stick
and go to Troubleshoot, it lists OS's it finds on the machine.
How does it find these OS's?
Presumably it looks through all the partitions on all the hard disks
for something that looks like an OS?
But how exactly does it identify an OS?

-- 
Timothy Murphy  
gayleard /at/ eircom.net
School of Mathematics, Trinity College, Dublin