[Leaplist] so, dead nv part?

[Bryan J. Smith]

Two (2) reasons for AGP mechanical issues ...

1)  Intel released the _wrong_ mechanical specifications pre-release

Unlike PCI and PCIe, AGP was a "trade secret" by Intel.  Accordingly,
only select vendors got the mechanical specifications.  Guess what?
Intel changed them in the final spec, putting pin spacing off 25 mils from
some specs -- a full pin -- for the placement of the slot to the end of the
board.  So the "hard to get" specs were plagued by out-dated info,
things that would be a no-brainer if they were part of an open spec
available to all vendors.

2)  AGP pin spacing is tiny

AGP is actually 32-bit PCI with all sorts of extra bus logic that fits in a much
smaller space than PCI.  So it uses half the width (25 mils IIRC) of PCI, and
it two-rows of pins.

[ Hence why PCI-Express uses Serialized I/O, to cut the pin-count down. ]

Additionally, AGP always had issues with the original "universal slot" design.
It was designed to both 3.3V and 2.5V cards could be supported, including
a possible, future drop (which would later be 1.8V).  Unfortunately, if 1.8V
card was not 2.5V compliant, the original "universal slot" definition would fry
an 1.8V only card, and often destroy the slot/mainboard with it (did it myself ;).

Now as far as AGP v. PCIe video cards, it's all about the interface on the GPU.

AGP is 32-bit parallel PCI, with special "local bus" connections for special
port and memory access (e.g., Direct in-Memory Execution -- D[i]ME).

PCIe is serial PCI (up to 16 channels), and relies on different mechanisms
for in-Memory Execution (far more reliable/compatible, with caveats).

They are completely different beasts.  A GPU must be either AGP or PCIe
as they are radically different in many aspects.

Only one bridge type was ever created -- a PCIe x8 to AGP by Intel.
It was used early on for bridging AGP cards to PCIe x8, and they were
slower in PCIe because the AGP features were lost -- e.g., NV40.
It can be used the other way as well, but then PCIe doesn't provide those
AGP features either -- e.g., NV45.

However, both AGP and PCIe can be far more easily bridged to PCI.

AGP is directly just 32-bit @ 66MHz SDR/DDR/QDR (66-266MHz effective)
and 133MHz DDR/QDR (266-533MHz effective), so slowing down to PCI
33MHz (or even PCI-X 66MHz SDR/DDR) is cake.  Other feature pins are lost.

PCIe is PCI as well, but serialized.  So it merely just needs to be converted
from serial to parallel.  Intel sells a series of IXH chips that convert up to
eight (8) PCIe channels into up to 64-bit PCI-X 1.0/2.0 at 66MHz SDR/DDR/QDR
(66-266MHz effective).  So doing 32-bit PCI at 33MHz is nothing.

Hence why still see 32-bit PCI options with GeForce 8400 and even a 9500
card, often universal 3.3V and 5V (because it's converted down much lower
anyway).



----- Original Message ----
From: Kevin Korb <kmk at sanitarium.net>

Those are all good suggestions especially re-seating the AGP card.  Those
things are way more picky than PCI cards in my experience.

I just wanted to point out that they still make AGP video cards.  I bought
one not long ago.  They just don't make them in the latest greatest
chipsets.

The last time I had a power failure one of my AGP video cards was dead
when it came back :(  And yes, that system was on an APC SmartUPS.

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