Web Farm: It is a multi-server scenario and we can keep servers separately. If the load on one server is in excess then the other servers step in to bear the strength. Server Load is based on various following models.
1. Round Robin. (All servers share load equally)
2. Network Load Balancer (economical)
3. HLB (expensive but can scale up to 8192 servers)
4. Hybrid (2 and 3).
5. CLB (Component load balancer).

We can implement web farms in .NET. Open web.config file and add mode options.
i) if mode=inproc (non web farm but fast when you have very few customers).
ii) if mode=StateServer (for web farm)
iii) if mode=SqlServer (for web farm)
Whether to use option (ii) or (iii) depends on situation. StateServer is faster but SqlServer is more reliable and used for critical applications.

Web Garden: It is a multi-processor setup i.e. in case of a web garden we have a one server having more than one processor. You can use web gardens in .Net as: Open web.config file and add webGarden = true in processmodel tag.