On May 17, 2013, at 10:32 AM, Bob Armstrong wrote: I thought the DELQA did? I don't think the DEQNA did, however. Also, the DEUNA and DELUA handles it, as far as I know. I thought I remembered that the Ethernet interfaces could do it, but how does that work? The DMR required that you have a M9312 with the appropriate boot ROMs - were there NI boot ROMS for the M9312 too? How did the DELQA do it (i.e. which QBUS PDP-11 CPU had an NI boot ROM)? Also, the DMR was smart enough to implement DDCMP in "hardware" and so it understood MOP at least well enough to detect the TRIGGER message. The DEUNA/DELUA/DEQNA/DELQA has no reason to implement DDCMP, although it certainly had enough local CPU power to do so. Did it still scan for MOP trigger messages anyway? Or was the Ethernet trigger implemented differently? MOP is a protocol that's defined both for point to point links (DDCMP) and Ethernet, though some bits (like Sysid) apply only to one of those. But the Boot message (NCP TRIGGER) is common to both. The implementation of the boot message depends on machinery outside the CPU that can recognize and validate the boot message, and make the CPU reboot. So it's not very common -- boot support doesn't make any sense in a software DDCMP implementation, or a software MOP on Ethernet implementation. The reason is that it would only work if the software on the CPU is sane, which is precisely when you do not need to force a boot. So you only see it on controllers that have their own microprocessor to implement that part of MOP, and they need the ability to force a CPU restart from where they sit on the I/O bus. Unibus does that; I forgot if Qbus does. DMC and DMC have the necessary microprocessor, as do UNA and LUA. QNA does not. LQA has a microprocessor and could do this in principle, but I'm not sure if it actually does. KMC could, if it wanted to, but here too I don't know if anyone has done it. Note that downloading a system is separate from boot/trigger. Download requires a boot rom that talks to the network device to speak the MOP Load protocol. You can do that whenever the system restarts; it might be because of a power fail or crash. Conversely, it's possible for a MOP Boot (trigger) to reset the CPU and have that result in a boot from local storage, such as disk or tape. That's probably not common but the two operations are separate and it's certainly valid for that to be the result. paul