Backup Exec Gold Edition can be purchased based on Front End Tera Byte(FETB) or the number of instances. When Licensed based on instance it needs to be purchased in group of 10 where a instance can be Win , Linux , unix , NAS instance , VM , physical instance, cloud instance. For example if there is 20 TB of data with 18 instances(physical, virtual ,cloud , win , linux , VM).
It can be either licensed as 20 FETB of Gold Edition (FETB based)
or 2 Bundles of Gold Edition (instance based)
Hope it helps !!!