On 2015-06-20 22:29, Hans Vlems wrote: > My question was whether the 11/20 had support for 18 bit addresses. I thought that the 11/20 was the only model limited to a 2^16 address space. Any PDP-11 without an MMU is limited to 64K of memory. There are several models without MMUs, so it was not only the 11/20... Johnny