difference between AGP 1x, 2x, and 4x?

[Sunny129]

i have a Voodoo5 and i just recently installed their latest beta drivers (v1.04.01 beta i think). there are quite a few more items to tweak in these drivers than there were in my old ones (v1.03.00). anyways, one of the new tweaks in the latest beta drivers is the ability to set AGP 1x or 2x directly through the drivers. i noticed mine was set to 1x, so i figure that i've been using this option for quite some time now. i switched it to 2x and played some UT. i didnt notice a difference. now i've heard a thing or two about it, but i dont really know what it is or what it does. can someone explain to me?

Eric

 

[Actaeon]

my old post

 

[Sunny129]

thanks for the link Actaeon, but it still doesnt explain what AGP 2x or 4x is. can someone explain to me what exactly it is? and also, i heard that Voodoo users can only use up to 2x, no matter if its running on a mobo that supports 4x, due to video card limitations. am i wrong about that? please give me your info. thanks

Eric

 

[BFG10K]

For the Voodoo there's no real difference between the settings. Just set it to AGP x 2 and you'll be fine.

 

[duragezic]

I believe Voodoo users can only set it to 2x because 3dfx never made it 4x compatible. Not that it matters though because virtually all games and programs have no benefit from agp 4x.

 

[Sunny129]

yes, i also hear that there is little performance difference between AGP 2x and 4x when it comes to gaming, but i am still confused as to what it really is. is it the speed at which data travels across the AGP interface? as for 3dfx's VSA100 chips, they are AGP 4x compatible (at least the Voodoo 4, 5, and 6 series). as long as the BIOS allows the user to set the AGP Xx, the Voodoo series 4 and later will run at AGP 4x. unfortunately for me, i have a CUSL2 mobo, and once i hit 140 mHz FSB or higher, the BIOS defaults to AGP 2x, and cant be pushed higher. maybe there will be a fix for this in future CUSL2 drivers. at the present time i dont even think there is a BIOS option on the CUSL2 that allows the user to change from AGP 2x to 4x. either that or i am overlooking the setting in BIOS.

 

[JONNYROTTEN]

YOU GUYS DONT GET IT ITS A MULTIPLIER( 1X 2X 3X 4X ) THE HIGHER YOU GO ON YOUR BUS SPEED THE HIGHER YOUR AGP AND PCI SPEEDS GO ALSO THE MULTIPLIER CUTS IT SO THAT IT RUNS AT THE SPEED IT NEEDS TO BE AT..

 

[thegreatjeff]

The x4 or whatever is I *think* (I'm no expert) that it's the speed it goes from vid card => hard drive or whatever.

 

[BenSkywalker]

AGP works on either SDR, DDR or QDR principles. The bus is always moving at 66MHZ(unless overclocked), but can send one(1X) two(2X) or four bits(4X) of information per cycle.

AGP 1X= 266MB/s

AGP 2X= 533MB/s

AGP 4X= 1066MB/s

Current PCI= 133MB/s(sticking to mainstream PC stuff)

Also, with PCI that 133MB/s is shared between all the various PCI devices, unlike AGP which operates on its' own bus. With some current mobos having six PCI slots that 133MB/s can shrink quite quickly on a per device basis.

Utilizing higher AGP rates for most current systems and uses isn't too great, texture swapping is limited both by AGP's peak rate, and also the fact that with 133MHZ SDRAM, you are at the theoretical peak if everything else is idle.

The main advantage is in very heavy geometry loads(well beyond games). Geometry data is uploaded to your video card via the AGP bus, AGP 1X is limited to around 6-7 million vertices per second(vertices are the points used to make polygons), 4X ~between 24-28million per second. For reference, Quake3 has about 13,000 vertices per frame on average(you would need to be pushing about 450FPS for AGP1X to be a complete bottleneck, give or take).

 

[Sunny129]

thanks BenSkywalker, thats the best explanation of what AGP Xx is and what it does.

 

[BFG10K]

I was going to post this last night but the server was having problems.

YOU GUYS DONT GET IT ITS A MULTIPLIER( 1X 2X 3X 4X )

3X? LOL!

THE HIGHER YOU GO ON YOUR BUS SPEED THE HIGHER YOUR AGP AND PCI SPEEDS GO ALSO THE MULTIPLIER CUTS IT SO THAT IT RUNS AT THE SPEED IT NEEDS TO BE AT..

I think you're a little confused here. It's nothing to do with bus speeds or PCI.

AGP x 1 is 66 MHz with one transfer per clock.
AGP x 2 is 66 MHz with two transfers per clock, which is essentially 133 MHz.
AGP x 4 is 66 Mhz with four transfers per clock, which is essentially 266 MHz.

The speed doesn't increase. AGP always runs at 66 MHz.

 

[RobsTV]

I think he was confusing FSB and PCI/AGP bus relationship.
66Mhz FSB = 33MHz PCI or 1/2, and AGP would be 2x PCI or 66Mhz. PCI bus 2x = FSB.
100MHz FSB = 33MHz PCI or 1/3, and AGP would be 2x PCI or 66MHz. PCI bus 3x = FSB.
136MHz FSB = 34MHz PCI or 1/4, and AGP would be 2x or 66MHz. PCI bus 4x = FSB.
Has to be something along these lines, as 3x AGP doesn't exist.