Applied and got an invite for a phone interview several weeks later. They asked me about experience I had on my CV and then asked me some technical questions about C++ and computer architecture. The questions were just covering the basics so if you've had some real world C++ experience (probably 6 months at least) you should know the answers.

The computer architecture questions were also just covering the basics but you should have at least done a small course in architecture beforehand.

Then I got invited for an assessment day, most of which was just hearing about the company and stuff, fairly relaxed. There was a group project with a Lego mindstorms kit where you were assessed but I don't think that part would have a large bearing on your application. This was followed by a 1.5 hour interview where they asked me a few more technical questions on C++ and architecture, which I thought was easier than the phone interview.

Overall very positive experience, but some drawbacks were that it took two weeks to hear back when I made my application and the assessment day was nearly eight hours long! I think the assessment day should definitely be cut down to maybe four hours as it takes up your whole day.