Harvard v. von Neumann

According to my reading, the Burroughs B5000 and Manchester Atlas were both Harvard architecture machines, and the GE-645 was von Neumann. Am I correct in my interpretation? << Technically none of them can be pure Harvard architecture because the operating system can write to memory (to load the program) and then start executing instructions from the same memory. When the 645 was running Multics (ie its normal status) then, like the other two, the user programming model had execute (+ read) -only code segments and thus would have the Harvard principle of non-self-modifying code. However, the hardware of both the Atlas and the 645 could, in theory, run with a user-writeable code segment ... I think that the B5000 would need tags explicitly to be switched to do such tricks. Andy