Overview of Pentaho architecture and components

Hello,

Our company wants to start using Pentaho. is there any Document that explains the architecture and components of Pentaho (such as the components of the BA server, DI server, repository/is)
I found some good documents, but they are describing the tools (analyzer, interactive report, dashboards, etc...).
I am not looking for a detail-technical description, just a general overview like:

- Which component is responsible for what or
- What is each BA or DI server-components responsible for or
- Which part of the repository is for what responsible


Can anyone help?
Thanks in advanced