MOSS 2007 Physical and Applicaiton Architecture Tiers

MOSS 2007 follows a 3 Tier structure

1. Web Server Tier (IIS) - can be network load balanced

2. Application Server Tier 

• Contains Shared Service Provider (SSP) which handles:
• Search, Index, Audience, User Profiles, My Sites, BDC, Excel Services (Last 2 are Enterprise Edition only).  Typically you woudl put My Sites on its own server, Excel Services/BDC on its own or the same server, and Audience/User Profiles on its own or the same server, and Search+Index on its own or the same server (if you had 4 servers in this tier for example).
  
• NOTE: Any service can reside on any mid tier server.  Also, the index server is limited to 1 per SSP, but all the other services have no limit as to how many servers can provide/service/host them 

3. Database Tier - consist of standard SQL Server 2005 or SQL Server 2005 Cluster of servers