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so ... AGP { 1x, 2x } = PCI (o'really?)

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DiTBho:
I've always wondered - was/is AGP only ever used for graphics cards? - (never seen ... say AGP-SCSI-HBA? AGP-optical-ethernet? ... )

Found this interesting answer  :o :o :o

DiTBho:
I will buy an AGP(1)-PCI adapter to make good use of an - otherwise - unused AGP slot.


(1) AGP 2x

DavidAlfa:
Not same as PCI at all.
The main reason these graphics buses existed (vesa, agp..) was to provide a dedicated bus, PCI shares its bandwidth with all devices, these don't.
Then AGP 1.0 was already 2x faster than PCI.

DiTBho:
say,

AGP = exclusive channel
PCI = bus

timing and signal protocol are similar... and =< AGP-2x electrical signals also seem compatible


--- Quote from: DavidAlfa on March 27, 2023, 06:01:03 pm ---bandwidth

--- End quote ---

but this comment is exactly what I have always wondered

--- Quote ---so it is just about bandwidth (and maybe latency) of AGP, or is it exactly about separate, non-coherent channel to system RAM?

"Non-coherent" means for me that it bypasses routing (in PCI, DMA might be targeted to another device and not necessarily system RAM) and bypasses cache coherence (DMA writes must at least invalidate cache lines that contain data the DMA writes to, and DMA reads must suck data from caches in writeback mode).

--- End quote ---

(my evil plan is to make good use of a 2x AGP slot with a PCI-fpga card  :o :o :o )

DavidAlfa:
PCI works at 33MHz, AGP starts at 66, so no way.
I guess you're making some kind of vintage adapter...?
Otherwise, why using something so old?

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