Ewald Cress explains how SQLOS tasks come into being:
The above system tasks wear their purpose on their sleeves, because the function pointer in the SOS_Task::Param is, well, to the point. The tasks that run user queries are more abstract, because the I/O completion port listener can’t be bothered with understanding much beyond the rudiments of reading network packets – it certainly can’t be mucking about with fluent TDS skills, SQL parsing and compilation, or permission checks.
So what it does is to enqueue a task that speaks TDS well, pointing it to a bunch of bytes, and sending it on its way. Here is an example of such a dispatch, which shows the “input” side of the WorkDispatcher:
Read the whole thing.