Pictures of an KDJ11-BF (was KDF) ??

Your advice confirms my experience as well. The reasons that the PDP-11/83 is faster than the PDP-11/73 are due to the use of PMI memory and the 18 MHz crystal on the KDJ11-BF as opposed to the 15 MHz crystal on the KDJ11-BB. I did a few timing tests with all of the configurations. As expected, the 18 MHz crystal added very little to the extra speed - my experience was that less than 1/3 of the increased speed was due to the faster clock rate. Obviously, most of the increased speed was due to the use of PMI memory which, as Pete specified, is available with an ordinary KDJ11-BB in addition to the KDJ11-BF. As far as I remember, the firmware on the J11 chip had to be revised to support the use of the 18 MHz crystal along with the FPF11 chip. The original firmware on the J11 chip could handle the 15 MHz crystal, but not the 18 MHz crystal. While the so-called floating point bug on the original DEC KDJ11-BF was not as wide known as the Intel floating point bug on the early Pentiums, the internet was not as developed either. Can anyone else confirm this information? Jerome Fine