I believe all the boards listed below are the various varients of the /53 and /53+. It was commonly used in DECservers 550's which explains the LAT ROMs listed on some of them. One of those can be converted to a PDP-11/53 by replacing the ROMs with PDP-11/53 ROMs. Logically with the memory onboard it should be faster than a /73, however, IIRC, there is something about it that makes it slower. Zane M7554 KDJ11-DA Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, LTC M7554 Refs: EK-KDJ1D-UG M7554-01 KDJ11-DA Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, LTC (VE) M7554-01 Refs: EK-KDJ1D-UG M7554-02 KDJ11-DB Q 11/53-PLUS CPU M7554-02 (J11 15MHz, 1.5-Mbyte RAM, 2 SLU, LTC) M7554-02 Refs: EK-KDJ1D-UG M7554-04 KDJ11-DD Q J11 CPU 18MHz, 1.5-Mbyte RAM, 2 SLUs (CSS) M7554-04 Refs: EK-KDJ1D-UG M7554-PA KDJ11-SA Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, S-box handle M7554-PA Refs: EK-KDJ1D-UG M7554-PB KDJ11-SB Q J11 CPU 18MHz, 512-Kbyte RAM, 2 SLUs, LAT PROM, M7554-PB S-box handle M7554-PB Refs: EK-KDJ1D-UG M7554-PC CMR53-AA Q J11 CPU 18MHz, 512-Kbyte RAM, 2 SLUs, S-box handle M7554-PC CMR53 boot PROM M7554-PC Refs: EK-KDJ1D-UG M7554-SA KDJ11-SA Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, S-box handle M7554-SA (VE) M7554-SA Refs: EK-KDJ1D-UG M7554-SC KDJ11-SC Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, S-box handle M7554-SC (VE) M7554-SC Refs: EK-KDJ1D-UG M7554-SD KDJ11-SD Q J11 CPU 18MHz, 1.5-Mbyte RAM, LAT ROM, S-box handle M7554-SD Refs: EK-KDJ1D-UG M7554-SE KDJ11-SE Q J11 CPU 18MHz, 1.5-Mbyte RAM, 2 SLUs, LTC, M7554-SE S-box handle M7554-SE Refs: EK-KDJ1D-UG M7554-YA KDJ11-SA Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, LTC, M7554-YA no handle M7554-YA Refs: EK-KDJ1D-UG M7554-YB KDJ11-SB Q J11 CPU 15MHz, 512-Kbyte RAM, 2 SLUs, LAT PROMs, M7554-YB no handle M7554-YB Refs: EK-KDJ1D-UG