To scale vertically (or scale up/down) means to add resources to (or remove resources from) a single node in a system, typically involving the addition of CPUs or memory to a single computer. Such vertical scaling of existing systems also enables them to use virtualization technology more effectively, as it provides more resources for the hosted set of operating system and application modules to share. Taking advantage of such resources can also be called "scaling up", such as expanding the number of Apache daemon processes currently running. Application scalability is the improved performance of running applications on a scaled-up version of the system.
A lot of Sitecore documentation I have been reading has been implying that separating out Sitecore instances into dedicated roles (such as Content Delivery and Content Management) is part of Vertical scaling. After isolation, you can then additionally add resources to each role to scale even more. Adding more RAM to a Content Delivery instance is clear Vertical scaling, but is the fact I separated Content Delivery from Content Management also Vertical?
From my perspective, this seemed like doing Horizontal scaling in order to support Vertical scaling. Am I wrong in this?
NOTE: I do know that you can also run some roles behind load balancers and thus also do horizontal scaling in that manner, I am interested more in the classification of role dedication.