max number of server processes

Hi,

afaik, we have two ways of increasing the performance of a server.

1. to increase the server processes on the same instance. i.e. horizontal scaling

2. to increase the number of dialog instances..vertical scaling.

so now we need to start with horizontal scaling..i.e. how many server processes we can define for a particular instance. Is there any hard and fast rule for that?

and when should we go to vertical sizing?

could someone please clarify?