Minimum specification to create 3 -tier architecture

Hi Exports

I need some clarity on the 3 - tier (i.e. Intelligence Tier, Processing Tier, Application Tier) architecture.

1. In which scenario can move from 1 - tier to 3 - tier architecture?

2. Is it possible to create 1 Intelligence Tier, 1 Processing Tier, 1 Application Tier? If no..What is the minimum dedicated servers need to be create for Intelligence Tier, Processing Tier, Application Tier?

3. If there are more than 500 concurrent user, it is recommended to create additional Application Tier. Likewise in which scenario need to create multiple

Intelligence Tier and Processing Tier?

Thanks in advance..

Regards,

Raja