OK, I did a search and miraculously was able to come up with the post I was referring to. It's a post by poena.dare titled A Tale of Three AIs and One Mad Scientist and it's an absolute must-read. I'm not going to go into all the details, nor am I going to attempt to verify all the suppositions involved, but this is a comprehensive essay based on Marathon cannon, primarily from terminal backstory. First of all, I had it backwards - Durandal was the oldest of the AI's and first installed on the Marathon, followed shortly by Tycho. Leela was the last to be installed and was shipped directly from Earth, rather than being assembled on Mars. If we believe the essay, Strauss placed numerous blocks in Durandal's programming to prevent him from getting out of control. It seems reasonable that he would have taken precautions with his hardware design as well. The interesting thing is that Marathon's personnel would have seen Durandal as being nothing more than a servant AI - the least capable and least advanced of the 3 - he was relegated to performing automated functions throughout the ship. Tycho was supposed to be the more advanced of the two. The reality of course was that Durandal was Strauss' pet project and the most advanced of the three.
So how to make him seem unimportant but yet give him the facilities needed to take over when necessary while at the same time keeping him in check? I would imagine that Strauss would design his hardware as a series of small, nondescript unobtrusive cores scattered about an area. The bobs would not even know that all of the separate cores were interconnected and would assume that only one and not all of them housed Durandal. Strauss could also keep Durandal in check with physical constraints that could separate components of his thought processes from each other if necessary. A plus would be that Durandal would be naturally redundant and could weather sabotage of only a part of his core. To me, then, I believe that the layout of level 5 would be perfect for what I would perceive to be Strauss' approach to Durandal's core.
