352 Part 2½ Regions of Computer Space Section 4½ Multiple-Processor Systems

that no addressability changes may be made without the approval of the operating system. All entries to the kernel, whether by interrupt or user request, force the assertion of both space bits.

To allow direct addressability, two of the relocation registers in (1,1) space are disabled, one each for the Mlocal page and the peripheral device control-register page. With these registers disabled, addresses that would normally be mapped are passed along the Unibus unchanged to be received by the addressed