pdp-11 ethernet boot

It depends on what you mean by "standard". The protocol is of course defined precisely, that is the MOP protocol. You can implement your own MOP server in a few days from that document. What the data means is entirely up to the client. MOP is basically a data transfer protocol, similar to TFTP; it doesn't say what the bits mean. There is the "parameter load" message with fields that have names suggesting some meaning, but even there what the client does with those is up to the client. There is no standard for any of this that I'm aware of. Yet another question is how the data is stored on the server (if at all). Since the typical use of MOP is to load a bare metal software image, a logical way to store it on the server is in the form of a linker output file for such a bare metal image. I think that you'd typically find a ".sys" file used that way. Here too I'm not aware of any standard. There proably were some conventions since the developers responsible for the client software would have to know how to package up that software into kits that could be installed on servers. But I never saw any documentation for that. As far as using a.out, sure, that could work. The real question is how you build the software that you want downloaded, and what the client side loader is looking for. If the client side starts with a secondary loader request, you can use that load a loader of your own that brings across the bits in whatever way you like. For that matter, if you prefer TFTP you could load a TFTP client... :-) paul