I got a very rough description of how it worked, but that was about it. No, the KS11 was long gone by later Vn. Also,I think not all of the -11/20 UNIX machines had it, just some. Actually, there is a PDP-11 version prior to V2, canonically called V1. The PDP-7 version seems to be called 'PDP-7 UNIX' or 'V0'. Normally, yes. I have the impression that one could finagle RK03's to work on the RK11-D, and vice versa for RK05's on the RK11-C, but I don't recall the details. The main difference between the RK11-C and -D (other then the implementation) was that i) the RK11-C used one line per drive for drive selection (the -D used binary encoding on 3 lines), and ii) it had the 'maintenance' capability and register (al omitted from the -D). Yes, but it wasn't major. They both did 1500RPM, so since they used the same pack format, the rotational delay, transfer rate, etc were identical. The one peformance difference was in seeks; the average on the RK01 was quoted as 70 msec, and 50 msec on the RK05. They were sold on eBait along with an -11/20 that allegedly had a KT11-B. (It didn't; it was an RK11-C.) I managed to get them scanned, and they and the minimal manual are now in Bitsavers. I started working on a Tech Manual for it, but gave up with it about half-way done. No; I had that idea a while back, looked carefully, our V1 listings pre-date the KS11. Well, it allows 2^18 bytes of main memory, but the address space of the CPU is still2^16 bytes. IITC, it's two backplanes high, the TC11 is one. So more like the RK11-C... :-) Totally different; it's real paging (with page tables stored in masin memory). The KT11-B provides up to 128 pages of 512 bytes each, in both Exec and User mode. The KT11-C, -D etc are all segmentation, with all the info stored in registers in the unit. I got the impression that the KS11 was more a 'base and bounds' kind of thing. Noel