N - Tiers in SharePoint

Sharepoint limitations for acceptable performance

Guidelines for designing a server for good performance. Numbers given below is not hard limits.

Guidelines for site objects.
50,000 Site Collections per Content Database
1,50,000 Site Collections per Web Application
2,50,000 Web Sites per site Collection
2,000 Sub Sites per Web Site
5 Million Documents per Document Library
2000 Items per View
50 MB (Max 2 GB) per Document file Size
2,000 Lists per Website
256 Field Types per List
2,000 Columns per Document Library
4,096 Columns per List
50 Web Part per Page

Guidelines for people objects
2 million Users in Group per Web Site
5 Million User Profiles per Farm
2,000 Security Principal (Access Control List) per Web Site

Guidelines for search objects.
1 Search Index per Search Server
50 Million documents per Search index

guidelines for logical architecture objects.
1 Shared Service Provider for 3 Farms (max 20)
5 Zones (hard coded) per Farm
8 IIS App Pools per Web Server
50,000 Site Collection per Web App
100 Content Database per Web App
50,000 Site Collection per Database

Guidelines for physical objects.
1 Index Servers per SSP
Excel Service = No Limit
100 Content DataBase per Search server
8 Web Servers per Database Server
3 Web Servers per Domain Controller

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Planning and architecture for Windows SharePoint Services 3.0 technology

If you want to know more about planning and architecture for WSS 3.0, please visit the following link.

http://technet.microsoft.com/en-us/library/cc288426(TechNet.10).aspx

In this you can learn about,
Determine organization and user needs (Windows SharePoint Services)
Planning worksheets for Windows SharePoint Services 3.0
Plan Web site structure and publishing (Windows SharePoint Services)
Plan for content and search (Windows SharePoint Services)
Plan site and content security (Windows SharePoint Services)
Plan communication (Windows SharePoint Services)
Plan for site creation and maintenance (Windows SharePoint Services)
Plan for system requirements (Windows SharePoint Services)
Design server farms and topologies (Windows SharePoint Services)
Design logical architecture (Windows SharePoint Services)
Plan for authentication (Windows SharePoint Services)
Plan for and design security (Windows SharePoint Services)
Plan for performance and capacity (Windows SharePoint Services)
Planning and architecture for Windows SharePoint Services 3.0 technology summary
Downloadable book: Planning an Extranet Environment for Windows SharePoint Services
Plan for data protection and recovery (Windows SharePoint Services)

You can also download this from the below mentioned Url
Downloadable book: Planning and architecture for Windows SharePoint Services 3.0 technology