3 tier 3 layer architecture?

In architecture, tiers relate to 'platform' layers (sql server is a data tier, iis is a web tier), and layers relate to logical layers (presentation-, bussines-, data access-, data- layer).

In architecture, tiers relate to 'platform' layers (sql server is a data tier, iis is a web tier), and layers relate to logical layers (presentation-, bussines-, data access-, data- layer). There is an overlap between tiers and layers (for example, you can deploy the data layer to the data tier). You can choose to host multiple tiers on the same machines without impact on the architecture.

Combining layers goes against a 3 layer architecture. The relationship is that you deploy your layers on your tiers. In UML this is modeled in a deployment view.