I agree there needs to be a SYSGEN to be able to use all 3 * RL02 drives with the DL(X).SYS device drivers and the hardware handles ONLY 18 bit addresses for both the DYX.SYS and DLX.SYS device drivers. BUT the RLV11 and the RXV12 from DEC also managed to handle only 18-bit addresses. So the DSD box was completely compatible with the stock (distributed) V4.00 of RT-11. However, V4.00 code in DY.MAC contained the extra instructions to use a double-sided media which would probably have been called an RX03. And although those extra instructions had bugs (after all they had never been tested) and were removed by V5.00 of RT-11, I did fix the bugs and ran a DYX.SYS device driver under V5.03 of RT-11 using the DSD 8" floppy as a double-sided drive. In addition, I also added a bounce buffer in DYX.SYS so that a user buffer above 256 KBytes could be used with the 18-bit hardware addresses in the floppy.