Clarification R/3 4.6/4.7 and WebAs6.20/6.30/6.40

Hi all,

I would like to know the difference between the SAP R/3 system 4.6/4.7 and the WebAS 6.20/6.30/6.40.Whats the relation between them.Is SAP R/3 4.7 using WebAs 6.20 to run sap applications.Even the training version minisap 6.10/6.20 are Web Application servers.How do they differ from other servers.Pls clarify me in this regard.I'm a bit confused with all these versions.

Thanx in advance

Gopinath Venkatesan