Dec boards- what are they?

On 6/8/05, Paul Koning <pkoning at equallogic.com> wrote: I think the semantic problem we are having here stems from where one is starting. The question we've been answering is a real world question, "I have this random DEC board in my hand... what does it go in?" and your question presupposes a subset of that "I have this random DEC board that is only Unibus, Q18 or Q22. Which is it?" In practical terms, one can't always *know* it's only Unibus, Q18 or Q22, thus the efforts to answer the larger questions. I've frequently seen PDP-8 and other boards mixed together in piles. Even if one _knows_ that a particular source only had Unibus and Qbus PDP-11s (reducing the likely range of products), something like a board from an RK611 or an RKV11 does go _into_ a Unibus or Qbus PDP, but is not itself a Unibus or Qbus board - the bus-level compatibility is managed at the backplane level, *not* the board level (for example - the RK611 controller is a set of hex-height cards and a 9-slot backplane that, dismantled, looks much like a DD11-DK Unibus backplane and assorted Unibus cards. The backplane is typically labelled "RK611" as opposed to "DD11DK", but unless you are a DEC-head, that doesn't mean a whole lot. Superficially, without inspecting what pins the wires go to, the two backplanes look the same. The same thing goes for the cards... superficially, the board that's part of the RK611 that has the 40-pin BERG connector (can't remember the handle number) has a superficial resemblance to an RL11, a common Unibus controller for the RL01/RL02. Same connector, same color PCB, same size, similar component density. Unless you locate an identifying mark on the PCB that _says_ RL11 (and know what one is), the only way to be sure is by looking up the handle number in a manual or on the 'net). We really aren't trying to evade your question, but we are trying to let folks know that barring a numeric list of products, there is no short list of easy-to-follow rules that _definitively_ distinguish a particular DEC board as exactly one bus type or another. There are rough guidelines that can help you eliminate certain obvious mismatches, but in the end, what ends up happening is that people like myself that have worked with DEC equipment over the years either _know_ what it is because we've seen one before, or we go look it up. I myself, with DEC experience going back to 1982, have misidentified things I've seen at hamfests. One particular example was, IIRC, mistaking the floating point board set for an 11/34a for some Unibus CPU. Now... in terms of your specific question, it wasn't like I thought it was a Qbus board set (being hex-height and all), but I had to look at it for a moment to discard some of the more common possibilities (OMNIBUS, primarily, something I _do_ go looking for at shows).