Harvard v. von Neumann

Sridhar> [I tried to send this before, but I don't think it went out. Sridhar> My apologies if you're seeing this a second time.] Sridhar> According to my reading, the Burroughs B5000 and Manchester Sridhar> Atlas were both Harvard architecture machines, and the Sridhar> GE-645 was von Neumann. Am I correct in my interpretation? I don't know the GE, but the Burroughs mainframes are v.N. Perhaps you got that interpretation because code is distinguished from data. But that's not by memory space; code (and for that matter other non-data things like pointers) is identified by "tag" bits which are stored in memory along with the data bits of each word. For example, data has tag 0, while executable code has tag 7. That gives you some protection. (Indeed, that's about all the protection you get; OS security in Burroughs mainframe systems did not come from the hardware, but rather from the fact that creating code files was a privileged operation, and only compilers were privileged to do that, and the ESPOL compiler was protected so Joe User couldn't use it.) You can find more on Bitsavers; there are a bunch of B6700 manuals there including the system reference manual. paul