Logical Layers vs. Physical Layers

Logical Layers vs. Physical Layers (Distributed)
Logical Layers and Physical Layers are the ones that confuse people. Firstly, a logical layer means that layers are separate in terms of assembly or sets of classes, but are still hosted on the same server. Physical layer means that those assemblies or sets of classes are hosted on different servers with some additional code to handle the communication between the layers. E.g. remoting and web services.

Deciding to separate the layers physically or not is very important. It really depends on the load your application expects to get. I think it's worth mentioning some of the facts that might affect your decision.

Please DO note that separating the layers physically WILL slow your application down due to the delay in communicating between the servers throughout the network, so if you are using the physical layer approach, make sure the performance gain is worth the performance loss from this.

Cost for deploying and maintaining physically separated applications is much greater. First of all, you will need more servers. You also need network hardware connecting them. At this point, deploying the application becomes more complex too! So decide if these things will be worth it or not.

Another fact that might affect your decision is how each of the tiers in the application are going to be used. You will probably want to host a tier on a separate server if more than 1 service is dependent on it, e.g. You might want to host business logic somewhere else if you have multiple presentation layers for different clients. You might also want a separate SQL server if you have other applications using the same data.