You can use one ViennaKey for all of your VIENNA INSTRUMENTS Collections if you want, as long as you run them on one machine. Of course you can also run several Collections on more than one computer, e.g., Solo Strings and Chamber Strings on Computer A and Orchestral Strings and Brass on Computer B. This will require the purchase of two ViennaKeys, one for each computer. This way you can distribute your Vienna Instruments as you wish over several computers. You can also move the licensing information from one ViennaKey to another, but you cant have the same Collection on two ViennaKeys at the same time.