Others already answered the boot ROM part. As for the protocol, MOP arrived first on DDCMP, and yes, that includes load/dump. If anything, it's primarily load/dump. The Sysid stuff is specific to Ethernet. I think DDCMP MOP also has MOP level loopback, using MOP packets which are different from the 90-00 Ethernet loop protocol. In DDCMP, MOP is a mode ("maintenance mode") -- same basic frame format but it's a datagram service as opposed to a connection oriented service. It's all spelled out in the specs ("maintop" which is MOP, and the DDCMP spec). paul On Feb 4, 2013, at 5:49 PM, Bob Armstrong wrote: An off the wall question that I m sure somebody on HECnet will know was it ever possible to download a boot image (e.g. RSX-11S) to a PDP11 over a DDCMP serial interface (e.g. a DUP/DMR/DMC or whatever)? Kind of like doing MOP over Ethernet, but without the Ethernet. Thanks, Bob