Today's question of the course (2780B), how do licensing options mix with multiple instances. The course points out the choices on installation;
- Per processor
- Per Server
- Device Client Access License
- User Client Access License
That's about it, but as always, MS-Licensing is more complicated than a single page in the text-book. If you want to know it all, there is an SQL Server licensing white-paper, covering;
- Virtualization / Multi-instances
- Multi-core processors
- Fail-over technologies (Cluster, Database Mirroring, Log Shipping)
- Multiplexing
- Separation of components over multiple servers.
- SQL vs Workgroup CAL's
- Special programs for ISV's and hosting providers
- Downgrading
For just Virtualization and Multi-instancing, read this section of the above white-paper. For more info on licenses and pricing, visit How to buy SQL Server. Keep in mind that pricing and licensing may vary based on your location.