how we can distributed these 3 categories (Client, AOS, Database ) in D3FO ?

In AX 2012 R3  we know that it's 3Tier Architecture.

Tier 1 : Client

Tier 2 : AOS

Tier 3 : Database

In D3FO , how we can distributed these 3 categories ?

Please give me more shed on this.

Thanks!