And I frankly wouldn't be surprised if most of those 10/100 cards were effectively behind a NuBus-ISA bridge, with no streaming burst transfer support. IIRC, your point about Quadras and NuBus 90 is correct. I think only the AV machines actually support it for CPU-card transfers, as opposed to card-card.
I just did get around to looking it up, and apparently I was wrong thinking "Nubus 90" was associated with the block transfer mode; apparently that's present in original NuBus as well, Nubus 90 is the secondary 20mhz clock. In theory at least a block transfer with NuBus 90 can approach 70mb/s. (But mostly in theory)
You put the answer to the question implied in your first sentence into your second sentence: the Q900 has FIVE NuBus Slots, the sixth port being taken up by the onboard NIC.
According to a block diagram of the Q900 the Sonic ethernet card in the machine does *not* reside behind the YANCC Nubus controller or the associated bus transceiver ICs. And for good reason; NuBus requires what was at at the time significant overhead in terms of decoding hardware to implement. It'd be pretty pointless to make a "motherboard" NuBus device for a whole slew of reasons. Here's a thing to keep in mind: Apple's "Slot" nomenclature actually doesn't *strictly* have anything to do with "NuBus", as in the electrical specification. Apple's nomenclature for slot addressing is basically an intentional callback to how slots are implemented in the Apple II. In that machine the full address bus is present on each card slot, so in theory a card can be "mapped" anywhere inside the 64k address space of the machine. However, each slot is *also* associated with a unique "window" in memory; an access to a slot's assigned address space triggers a select line unique to that slot. In the Apple II's case that meant that add-on cards, if they were simple enough that they could pack all their ROM and I/O space into a 256 byte window, could dispense with a lot of decoding hardware. (You could map a simple I/O chip directly on the data and lower address lines on the slot connector and use the slot enable line as chip enable. That's why it's not uncommon to see Apple II cards that literally only have one chip on them, like a 6821 PIO.)
In the Mac II
the hardware and firmware is set up in a roughly analogous manner; the address space of the CPU is chopped up in such a way that certain areas are "magically" associated with physical Nubus slot locations, and the physical Nubus controller is programmed to do the needful to route data appropriately when those locations are accessed *
when there's actually a NuBus controller/physical slot present*.
The same firmware and memory mapping conventions can and are also be used by motherboard and PDS devices that electrically have nothing to do with NuBus. "Designing Cards and Drivers for the Macintosh Family" strongly recommends that when designing 68030 PDS cards you take advantage of these "Psuedo-slots", because it allows the same firmware functions that allow auto-configuration of Nubus cards to control them as well.
Because the same firmware and memory mapping is used it's strictly speaking not really *possible* for a "Tattletech" program to tell if a device is on a physical "NuBus slot" (IE, behind the NuBus controller) or not. All it can really tell you is if a device is enumerated in slots 1-6 in the firmware and if its devices are residing in the associated minor, standard, or superslot range that matches that slot number. Presumably Tattletech does have some dictionary information present to say if the Macintosh it's running on has a Nubus slot in that area or not and could make the decision based on that, but maybe it doesn't make a distinction; if it's enumerated in the Slot Manager it's Nubus, regardless of what the wires really are.
(It's possible, I suppose, that the SONIC ethernet in the Quadra 900 *looks like* it's in the "missing" slot 6 of the machine, but I highly doubt it. The Q900/950 have PDS slots, I imagine it's expected to use the remaining assignment for its psuedo-slot. I don't think the motherboard devices in 68k Macs generally occupy "regular" slot numbers, since their drivers are in the main firmware, but there are probably exceptions; for instance, just off the top of my head I think the onboard video in an SE/30 is mapped as if it were a very brain-damaged NuBus video card. Again, though, could be wrong about that.)
Also, in case you're wondering, Trash,
the official ANSI 1196 limit on the number of NuBus slots is 16. Apple only supported a maximum of six because that's the most that would fit into the memory mapping scheme they chose for the Mac II, which dictated some nasty tradeoffs for compatibility with 24-bit addressing mode. (Another interesting thing in the PDF linked above: the original Apple Nubus implementation didn't support block transfers even at 10mhz. Did they enable that in later revisions?)
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