Let me preface all of this by saying I think we're splitting hairs...
incurable said:
Yes, exactly. PCBs are just a bunch of wires between multiple layers of plastics.
But my point is fairly simple: without that "bunch of wires between multiple layers of plastics," you don't have *any* interface between the host system bus, be it AGP, PCI, PCIe, or whatever, and your gpu. So obviously, the role of the pcb is critical. You seem to be quite detailed except when discussing the pcb, which you see apparently as inert and "just a bunch of wires between multiple layers of plastics"...
The gpu pcb (the pcb the gpu is mounted on), too, must support the host bus interface, right down to the connecting pins, or the gpu mounted on the pcb won't be functional in the host system. What is there in the gpu or substrate, for instance, that supports voltage changes and regulation from one host-bus standard to another (eg, the differences between AGPx1 (PCI66), x2-x4 and AGP x4-x8 )? All of that circuitry is extraneous to the gpu or the gpu substrate and is a component of the pcb on which the gpu and substrate is mounted. Clearly, the pcb for these products is "active" and critical in every sense of the word. In fact, I guess we need to make a distinction between gpu and gpu substrate, as that distinction also seems lost in the wash...
The bus interface unit is part of the GPU, it's on-die.
Which must be connected to the host bus via the pcb circuitry, otherwise there is a disconnect between the host and the gpu and the gpu will not function in the host system. The gpu connects with the gpu pcb which in turn connects with the pins in the physical mboard slot, the host system bus's electrical interface with the card.
WaltC said:
I'm still not sure which part you're referring to, are you referring to the flip chip carrier or substrate which the GPU die is affixed to?
I'm referring to the pcb on which the gpu is mounted. The gpu interfaces with the pcb, but the pcb interfaces with the host system bus. Instead of pcb, would you be more comfortable if I called it a "card", instead?
I'd expect them to have different codenames for every different pin-layout of the substrate, regardless of GPU and HSI combination used.
Think about all of the various PCI gpus nVidia did, and on how their nomenclature changed while still running on PCI--ditto, AGP. You might expect them do that, but I wouldn't, because all of their previous chips received numbers based on architectural differences--with gaps of "5" denoting newer architures. What was the difference between the substrate for nV30 & nV35, or nV35 and nV38, for instance? All were AGP x4-x8 reference designs, as I recall.
IMO, nVidia has departed from its traditional nomenclature by referring to an nV40 mounted on a PCIe-interfacing pcb as "nV45." Now, if they'd have called it "nV43," instead, I'd have had no comment, as it's only the "5's" that have traditionally denoted new nVidia architectures (eg., nV10, nV15, nV20, nV25, nV30, nV35, & nV40--nV30 & nV35 were both AGP x4-x8 reference designs, and nV35 happened as it did because nVidia cancelled nV30.) Which chip among those listed here was an exact duplicate of the one before, the only difference being its connection to the host system bus? That's my point.
Look at it this way: what is nV40 in terms of difference with nV45, as reported thus far? It's nV40 without the bridge, mounted on a pcb designed to electrically support and connect to an AGP x4-x8 host bus slot. nV45, then, is nV40 *with* the bridge, mounted on a pcb designed to electrically support and connect to a PCIe host bus slot. Pretty simple, it seems to me. Unlike the differences between nV25 and nV30/35, which were architectural quite apart from substrate considerations.
Quite frankly, I've never heard/read such comments from ATi, but it's conceivable that you could support all these modes with a single bus interface unit, as they're rather simliar. (PCI66 in that case probably equals AGP 1x without AGP texturing support)
Well, the info is still buried somewhere on the ATi site, I would presume, as ATi put it there circa R300, and I referenced it in similar threads here months ago. R300 would have been just as comfortable with PCI66 as AGPx8, according to ATi, but it's for certain you could not have taken an R300 mounted on an AGPx1 pcb and plugged it into an AGPx8 motherboard slot, could you? Voltage support and pins on the pcb are different--but the gpu is the same. Which was my point. ATi only offered the R300 in AGP x4-x8 reference designs, but that had nothing to do with what was theoretically possible to do with the vpu in terms of host-bus interface.
As I've written above, the bus interface unit is part of the GPU, it's on the GPU die, and the only function of the different pieces of PCB the die is affixed to is the channel the signals coming from/going to the die. R300 'talks' AGP to the outside world (at different speeds though, as you mentioned), as do R420 and NV40. For these designs, the outside world is the AGP interface of the chipsets northbridge.
But my point is that an R300 mounted on a PCI66(AGPx1) pcb can't do any "talking" to the outside world at AGP x8, unless the same gpu is mounted on an AGP x8 pcb which can handle the pin connections with the host bus and the differences in the voltages. This is why you can't say the pcb is irrelevant...
Now for the NV45 design it's a little more complicated, nVidia implemented the HSI bridge on the same carrier as the NV40_GPU, so the NV40_GPU 'talks' AGP (at an accelerated rate) to this bridge and the bridge then 'talks' PEG to the PEG interface in the northbridge of the chipset.
But it is *the same nV40* that's doing the talking, isn't it?...
I just don't see how you can say with a straight face that "there are no architectural differences between nV40 and nV45," which is true, and then add, "But the differences between the nV40 and nV45 reference design are not extraneous to the gpu"....
Make up your mind...