So I've got a Q-bus system with 64KW (128KB) of RAM that is allegedly an 18 bit backplane. When I'm in ODT I can type: @177770/ And enter values for 1777772, 1777774, 1777776, and then it wraps around to 000000. If I start at 200000 it works until 3777777 and then wraps to 2000000. So it seems to not cross a 64KB boundary. Also the boot area is 177300 ? so it is in the upper 4K of the 64KB address space, is it legal to have memory "above" the I/O page? --Chuck