Unkown purple plant

Can someone please indentify this plant for me. I've had it awhile and it doesnt seem to be thriving. I'd like to find out how to care this plant before it dies on me.

 

Sempervivum maybe 'Black Mountain'

try this site for comparison:

http://www.garden-of-mu.com/sempervivums/1-semp-framepage.HTML

 

Notice at the link provided that the 'Black Mountain' has its foliage rosettes down on the ground. I'd think since this specimen has trunks it would be an Aeonium.

 

Damn, thought I had one. Ron B is absolutely right. Sorry if my reply threw you off Lav, I'm new at this.
Maybe Aeonium arboreum var. 'atropurpureum f. nigrum'
See if this site looks better: http://davesgarden.com/pf/go/1930/

 

thanks, you guys were a big help!
much appreciated