Adobe ColdFusion Builder has a built-in ColdFusion Server, which is a lighter version of Adobe ColdFusion. This bundled version is the same as ColdFusion Express. See Installing ColdFusion Express.
While installing ColdFusion Builder Standalone (Not eclipse plugin), you will be prompted to install the bundled ColdFusion Server. During the installation process, you must provide a password for the bundled server. The password that you provide will be used for Administrator and RDS.
You can quickly build and debug applications using ColdFusion Builder and the bundled ColdFusion Express. When you are installing ColdFusion Builder, you will be prompted to install the bundled Server. When you choose to install the bundled Server, the Server gets installed under <CFBUILDER_HOME>/ColdFusion directory. For configuring the Server, see Installing ColdFusion Express.
So, if you are using ColdFusion Builder to quickly build and debug applications, you do not need to install ColdFusion Server separately.
The bundled ColdFusion Server runs on port 8600. If this port is not available, a different port will be used.