Protection Lookaside Buffer
On the Mill memory protection and virtual memory translation are separate systems. This allows, among other things, to make both protection and translation cheaper and faster by putting the protection structures on top of the caches and the memory translation below the caches. Actually there are two Protection Lookaside Buffers, iPLB and dPLB covering code and data caches respectively. The iPLB holds execute and portal call permission, the dPLB read and write access.