Very broadly speaking, technical interviews that I have attended (on both sides of the table) tend to come after the qualification stage - that is to say that you'll have already had some technical questions and successfully answered them.
In my experience there are a few stages - sifting questions at the telephone interview stage which are usually 2/3 very easy questions plus maybe a more challenging question to see how you answer. At a face-to-face you could expect to have some more relevant and challenging questions and these can be closed (testing your knowledge) or open (testing your approach). A technical interview tends to be a much more open forum where you're given a scenario and expected to talk through your solution and draw relevant diagrams etc etc.
In my most recent technical interviews, two were nearly identical in format - Split into two parts, I was asked to discuss an environment I had recently worked on (whiteboard diagram, design goals, challenges, outcome etc) and then basically design a technical solution to xyz problem.
The goal is to make sure that you know your stuff and that you have the sort of approach to the sort of things you'll come up against in the role to succeed. This obviously varies from role to role - design/project-focussed roles will demand very different skills to reactionary support roles.
To prepare, you need to be able to talk confidently about all of the common elements of everything you've listed in your CV,
especially where it overlaps with the things mentioned in the job spec. Don't think that because you're interviewing for a Windows role that you won't get asked an in-depth question about Unix if you've put it down on your CV. The interviewer might well have decades of Unix experience, you've no way of knowing.
To prepare for any open questions, try to think through how you'd approach a greenfield deployment of whatever technology or how you'd approach coming in blind to a new environment that's undergoing a major issue. You don't necessarily need to know anything at all about the technology here (though it helps...) but basic things like asking for the requirements or documentation, any plans for expansion or if changes have been made recently etc etc.
Some technical questions are there just to boost the ego of the interviewer. Don't sweat those questions, they're probably beyond the reach of most candidates anyway. Try not to let them upset your thought process for the rest of the interview
Good luck!
