On 05/20/2014 11:04 AM, Johnny Billquist wrote: M+ do not need split I/D-space. But you do need 512K of memory. But the 11/23 and 11/24 are supported CPUs. I have 1M of memory. Sure you're not confusing the 11/23 with the 11/23+? I was poking at 4.6M+'s SYSGEN and it wouldn't accept 11/23 as an answer. The difference between the 11/23 and 11/23+ is the amount of memory. The original 11/23 could not go above 256K... If you have more, then you actually have an 11/23+. In practice, though, the vast majority of systems out there that say "PDP-11/23" (not -PLUS) on the front are in fact capable of 22-bit addressing; you've gotta look at the etch rev of the CPU board. See my other email. -Dave -- Dave McGuire, AK4HZ New Kensington, PA