yes, AGP 8X (as multipler shows) should have to be twice as fast as AGP 4X. its actually not, its just ~10-40% performance increase. where it was expected to be 100%.
for your convinience, i'll describe all AGP standards on 32-BIT architecture.
PCI was 33Mhz @ 32-BIT register and has the data tansfer rate of 133MB/s
AGP was clocked @ 66Mhz with trasnfer rate of twice as of PCI, so 266MB/s
AGP2X =clock rate = 133Mhz, DTR= 532MB/s (Roughly) as it has capability to read on both rising and falling edges of signals.
AGP 4X = 266X4 = 1064MB/s (or ~ 1GB/s), clock rated at 266Mhz
AGP 8X = 266X8 ~ 2GB/s , clock rated at 533Mhz
and so does PCI-E = 16X ~ 1Ghz Clock rate and DTR ~ 4.15Gb/s
~ means not equal, but equalivent.
theoritically AGP8X was suppose to be twice as fast as AGP4X, but it isnt.
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