SharePoint Server 2010 comprises of three architecture areas that are inter-related in the design and deployment of implementation.

Physical Architecture
Hardware configuration broken down into a three tier model:
    - Web Front End for web applications.
    - Application for managing and serving service applications to web applications.
    - Database (SQL) for hosting databases used by web application and service applications.

Logical Architecture
Comprising of four distinct hierarchical levels:
    - Farm
    - Service Applications
    - Web Applications
    - Site Collections

Information Architecture
Strategy and plan for information delivery and access. The key layers are:
    - Managed Metadata Service and Content Types
    - Site Collection Model
    - Sites Model
    - Lists and Libraries
    - Taxonomy
    - Putability and Findability
    - Governance
    - Business Logic

For further help on planning and architectures - please visit http://technet.microsoft.com/en-us/library/cc261834.aspx