I think so (evidence detailed below). The support may not have been quite identical to that in V4 (e.g. there was no support for pure texts in V3 - below), though. This is the real problem, of course; all we have for V3 is some man pages. (And in relying on them, we have to hope that they were updated to match the then-current system - which is not guaranteed, but in general at this point in time, man pages do seem to match whats's in the code.) Without a lot more information, which is now almost certainly lost, we are unlikely to be able to tell. But let me start by laying out what we do know. To start with, it's important to realize that support for protection (and relocation - i.e. memory that looks, to user code, like it's at 0, is actually at, say, 060000 in physical terms) in PDP-11 UNIX pre-dates the -11/45. DEC had a rare, and now almost forgotten "Memory Protect & Relocate" option for the -11/20, the KS11: https://gunkies.org/wiki/KS11_Memory_Protection_and_Relocation_option What exactly it did, and how, is now uncertain (no documentation, or code that used it, appeats to have survived - all we have are a couple of vague recollections), but it is certain that that the UNIX group's -11/20 had it: https://www.bell-labs.com/usr/dmr/www/odd.html and Ken has said that he wrote the code to use it. It's also important to remember that not all the machines running UNIX would have had their hardware updated simultaneously: e.g. the patent group's -11/20 would not have needed the KS11 as much, since it was runnng mature applications. So UNIX was probably conditionalized to run with and without the KS11. As late as V3, there were apparently still UNIX machines without relocation hardware: "The purpose of this command is to simplify the preparation of object programs for systems which have no relocation hardware.": http://squoze.net/UNIX/v3man/man1/reloc When the support for the KS11 appeared is uncertain. It's not in the extant V1 code; but V2 seems to have had it: "the current system, which has relocation and protection hardware": http://squoze.net/UNIX/v2man/man5/core V2 also seems to have started looking forward to the -11/45 - "a trap is simulated by the floating point simulator" (ditto); "if they correspond to 11/45 floating point instructions": http://squoze.net/UNIX/v2man/man3/fptrap It is possible that they already had the -11/45 at this point, but I would tend to doubt it: "immediate mode ((pc)+) is not supported, since the PDP-11/45 handbook is not clear on what to do about it." (If they had it, a simple experiment would have produced the answer.) And "Double precision results are probably less correct than the hardware will be" (note tense). (All from v2man/man3/fptrap.) V3 seems to have the -11/45: "it depends on what hardware is present (EAE, floating-point option)": http://squoze.net/UNIX/v3man/man5/core The "floating-point option" would only have been on the -11/45. (And again we see that V3 still ran on -11/20's; the -11/45 would not have had an EAE: https://gunkies.org/wiki/KE11-A_Extended_Arithmetic_Element since all the EAE operations - except normalization, but that's only needed for floating-point - were in the basic -11/45.) Probably the protection and relocation provided to UNIX processes on the 11/45 was very similar to that provided with the KS11. Do note that thememory management was not exactly the same as V4's: "In the future the text segment will be write-protected and shared.": http://squoze.net/UNIX/v3man/man5/a.out However, it was keeping multiple processes in main memory at the same time: "only processes whose core images are on disk have visible names": http://squoze.net/UNIX/v3man/man8/ps So we can actually tell a fair amount about the evolution through V2 and V3 from the few scraps that are left to us. I do live in hope that a V2 or V3 listing will turn up one day; the system changed a lot in that period, and many questions aren't answered definitively by the man pages. (One big one is details of how the process' address space was laid out - ld(III) and exec(II) simply say nothing at all. I assume it started at 0 - but who knows? In V1, it must have started at a higher address - as on MINI-UNIX: https://gunkies.org/wiki/MINI-UNIX#Implementation_details which I am fairly familiar with - but again, neither V1's ld(III) or exec(II) mentions this detail. I suppose I could work it out from the V1 source, but I'm not that interested... :-)) It is possible that the evolution started with just protection (if the KS11 could do that), and relocation was added later. It seems clear that the step from the KS11 to the -11/45 was probably not large. If anyone has a V2 or V3 listing, please sing up! That would be an incredibly valuable thing to add to the historical record. Noel