Thanks Joe, John, and Bill. All comments together helped a lot! When you set DY disabled, the device is still known to RT11, so I renamed the DY driver extension to "sas" :-) However, DX keeps the CSR and vector which are not the defaults, so I changed them while running RT11. After the reboot, only DX is listed in ".sh dev" and the driver is installed! Breaking to SIMH and attaching a (new) disk container is easy, and the RT11 output is as expected. Below is the (copied) output. Now, I am keeping my fingers crossed ... I hope that SIMH writes the RX01 container file in the physical RX01 floppy disk structure. What I would like to do is creating an RX01 disk file on the PC, and then use Peter McCollum's RX11 emulator to transfer the RX01 disk file to a real PDP-11 RL02 cartridge. We'll see this evening! thanks! - Henk. sim> set cpu 11/70 sim> set rl0 rl02 sim> attach rl0 D:\Apps\simh_rt11\RT11work.dsk sim> set ry disabled sim> boot rl (booting RT11XM) .sh dev DX Not installed 177174 270 DY Not installed 177170 264 .rename dyx.sys dyx.sas .boot rt11xm.sys .sh dev DX Not installed 177174 270 .set dx csr=177170 .ser dx vector=264 .sh dev DX Not installed 177170 264 .boot rt11xm.sys .sh dev DX Installed 177170 264 ^E (break to SIMH) sim> attach rx0 testrx01.dsk RX: creating new file RX: buffering file in memory sim> c dir dx0: ?DIR-F-Invalid directory .init dx0: DX0:/Initialize; Are you sure? Y .dir DX0: 0 Files, 0 Blocks 486 Free blocks ^E sim> exit Goodbey RX: writing buffer to file This message and attachment(s) are intended solely for use by the addressee and may contain information that is privileged, confidential or otherwise exempt from disclosure under applicable law. If you are not the intended recipient or agent thereof responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify the sender immediately by telephone and with a 'reply' message. Thank you for your co-operation.