Let's look more in detail at a typical FAST Search Server for SharePoint 2010 deployment, and in particular at the Search Service Applications (SSAs) in such a deployment. SharePoint 2010 with FAST Search as the search provider will typically have two SSAs; the FAST Query SSA and the FAST Content SSA. Note that these two SSAs are differerent types of SSAs, i.e. of type Regular and ExtendedConnector respectively (useful to know if you want to script and automate setup).
The main reason for having two types of SSAs is the separation of content; People content is indexed and served by the SharePoint Server, while all other content (documents, sites, pages, etc) is indexed and served by FAST Search. Here's what their respective responsibilities are;
The figure below gives an overview of where the SSAs fit in the search architecture.
You can of course use PowerShell to list and update settings on the SSAs, e.g.:
You can find more details on the SSAs in the Deployment and configuration of FAST Search Server 2010 for SharePoint (Beta) documentation. More information on the Service Application Framework (SAF) can be found on MSDN, and in several blog posts here.