AGP compatibility question

[imported_Zor]

Will an AGP 3.0 (8x/4x) card work with a mobo that is AGP 2.0 (2x)? Are the cards backwards compatible?

 

[Bozo Galora]

Gets kinda messy with dif chipsets, dif card abilities to use single or dual voltages
AGP 2.0 is 2X 4X, 1.5V or 3.3V
http://www.motherboards.org/files/techspecs/agp20.pdf

(Quote)
AGP Graphic Boards on Intel i845 and i850 Chipsets [Update]

The Reason for Updating

In our recently (21st of October) published article dealing with this issue we tried to show an absolutely reliable method for definitely distinguishing 3.3V AGP2x graphic boards from 1.5V AGP2x/4x boards for the purpose of avoiding hardware damage when operating these graphic boards into i845/i850-based motherboards.

There was ample feedback of our readers, but merely little of the graphic board's manufacturers. Solely Hercules, unfortunately classified as concerned in that article, looked into the matter and was now able to point out that our demonstrated testing method is incorrect!

[AGP Graphic Boards on Intel i845 and i850 Chipsets]

http://www.hardtecs4u.com/reviews/2001/agp4x_e/index2.php
http://www.hardtecs4u.com/reviews/2001/agp4x_e/index3.php
http://www.hardtecs4u.com/reviews/2001/agp4x_update_e/

Summary of the Problem

1. At present there are various types of graphic boards on the market. Some of the actual models are pure AGP2x boards, some of them are capable of both AGP2x and AGP4x mode. These modes and their technical requirements are exactly defined by Intel's AGP2.0 Specifications.

Among others these specifications are prescribing a voltage of 1.5V for AGP4x graphic boards, whereas AGP2x boards may quite possible be manufactured for 1.5V or 3.3V working voltage.
Signaling Level- AGP 1x Mode- AGP 2x Mode -AGP 4x Mode
3.3 Volt .................yes.....................yes......................no
1.5 Volt .................yes.....................yes......................yes

2. Corresponding to the different AGP graphic boards there are different types of AGP sockets. While the AGP4x slot and the AGP2x slot are very seldom found, predominantly AGP universal slots are used in current motherboards. This slot allows to plug in easily AGP1x up to AGP4x graphic boards. These already demonstrated pictures show the difference in slot structure.

3. Current popular chipsets like Intel i815, VIA KT133(A), KT266(A), AMD 760(MP) etc. are supporting both AGP working voltages of 1.5 and 3.3V, whereas motherboards based on Intel's i845 or i850 chipset and nVIDIA's forthcoming nForce are unable to work with 3.3V graphic boards, absolutely requiring an 1.5V AGP graphic board for avoiding damage of both mother- and graphic board. For the same purpose it is compulsory to use only AGP4x slots on the concerned motherboards, yet applying to all available i845, i850 and nForce motherboards according to our present knowledge.

Unfortunately some manufacturers put AGP2x graphic boards with AGP4x-shaped plugs on the market, therefore fitting into AGP4x coded slots. This should be no problem as long as these graphic boards provide a signaling level of 1.5 Volt or are solely used in motherboards with the above listed 1.5/3.3V-compatible chipsets. But exactly this seems not be ensured in all cases, as there was feedback from motherboard manufacturers and users as well, informing about hardware damage after plugging such a graphic board into an i845 motherboard and therewith providing the basis of our article.

 

[cubby1223]

AGP 8x means by definition that it can run at 1x, 2x, 4, or 8x speeds.

The only issue is the voltage. There were some early AGP cards that were 3.3v only but had the 1.5v notches. Why? I haven't a clue. Outside of those few older cards (mostly TNT / TNT2 class cards), all others follow the proper notching & as long as that new card fits in the slot, it is compatible.

 

[imported_Zor]

Thanks for the help.

I checked my mobo manual and it supports both 3.3v (for 2x) and 1.5v (for 4x).