Can AGP 8X video cards be used on a motherboard with an AGP 4X / AGP v2.0 compliant port?

Yes.

Yes, it should work, the voltage is what matters. 99.9% if you can fit the card in the slot (without forcing it), it should work.

Here's a good read on AGP compatibility: http://www.playtool.com/pages/agpcompat/agp.html

BTW, be extra careful with AGP universal slots. They are sometimes not as compatible as they claim to be.

Thanks all for the quick responses!

Joseph_Joestar wrote on 2021-11-18, 14:14:

Here's a good read on AGP compatibility: http://www.playtool.com/pages/agpcompat/agp.html

BTW, be extra careful with AGP universal slots. They are sometimes not as compatible as they claim to be.

That's an excellent read! So, from what I understood, an AGP 3.0 card can potentially fit in an AGP 2.0 slot and not work, but only if it is not backwards compatible. And thankfully, all AGP 3.0 cards also support AGP 2.0.
As you said, the only problem is with a Universal AGP port that is only universal in slot and not in voltage - fits both AGP 2.0 and AGP 3.0 cards, but only supports the voltage for one of them. But that problem shouldn't apply to an AGP 2.0 port.

Great, thanks again!

some very late AGP 3.0 cards don't support the 1.5V from AGP 2.0 thats correct, It should be a very limited group of late ATI cards however that require .8V AGP 3.0, for 99% of AGP 8x cards they are 4x/8x and use 1.5/.8V AGP depending on slot. Some really late cards like the X1950Pro, HD3850, HD4650 ect may only support AGP 8x, but the thought behind it was more than likely only someone with an Athlon X2 in a 939 or Pentium D on 775 would be upgrading anyway and they are all AGP 8x

candle_86 wrote on 2021-11-22, 15:58:

some very late AGP 3.0 cards don't support the 1.5V from AGP 2.0 thats correct, It should be a very limited group of late ATI cards however that require .8V AGP 3.0, for 99% of AGP 8x cards they are 4x/8x and use 1.5/.8V AGP depending on slot. Some really late cards like the X1950Pro, HD3850, HD4650 ect may only support AGP 8x, but the thought behind it was more than likely only someone with an Athlon X2 in a 939 or Pentium D on 775 would be upgrading anyway and they are all AGP 8x

That's the first time I hear of an AGP 3.0 card not being compatible with 1.5V/AGP 4x signalling. I was under the impression all commercially avaliable AGP 3.0 cards were actually universal 1.5V AGP 3.0 cards.
Can you give me a link or something to look into what exact cards aren't?

well i havn't seen an HD4650 that mentions AGP 4x compliant, they all say only AGP 8x which leads me to assume they require .8 V

candle_86 wrote on 2021-11-22, 18:09:

well i havn't seen an HD4650 that mentions AGP 4x compliant, they all say only AGP 8x which leads me to assume they require .8 V

Thanks, I'll try and look into this. 😃👍
Has anyone got any experience with an HD4650 and AGP 4x?

candle_86 wrote on 2021-11-22, 18:09:

well i havn't seen an HD4650 that mentions AGP 4x compliant, they all say only AGP 8x which leads me to assume they require .8 V

According to Bjorn3D and a couple of other sites, the HD4650 supports AGP 8X / 4X:

• https://bjorn3d.com/2009/10/sapphire-hd-4650-agp/
• https://hexus.net/tech/items/graphics/19725-s … ower-agp-users/
• https://hexus.net/tech/news/graphics/19727-sa … radeon-hd-4650/

And here's an Amazon review from someone who used it on an AGP 4X motherboard: https://www.amazon.com/gp/customer-reviews/R1 … ASIN=B002MLZPBY