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# AGP Slot Signaling Voltages

### #1 Webslinger64 Posted 20 February 2009 - 01:05 PM

Webslinger64

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Hey folks...

OK, so I'm trying to understand the correlation between the signaling voltages of my AGP slot and the potential video cards that would be compatible with my set up. I've done some research on the Internet, but am still a little hazy. If somebody could clarify some things for me, that would be great.

Basically, my AGP slot is version 2.00, current AGP speed 4X. The way I understand it, I should be able to run any video card that is 4X/8X and even possibly an 8X video card because of backwards compatibility. However, the potential flaw to my understanding here has to do with the signal voltage my AGP slot is geared for. Near as I can tell it is 1.5V. I looked at this illustration

and matched my AGP slot to the second choice from the top titled 'AGP 1.5 V'

The way I understand it, AGP 1X/2X is 1.5V or 3.3V, 4X is 0.8V or 1.5V, and 8X is 0.8V specifically. I believe some AGP 4X slots are compatible with both 1.5V and 0.8V, but don't know if mine is. That's the question. If my AGP slot is 1.5V, does that mean it is compatible with a video card that is 1.5V and 0.8V?

A friend of mine bought a new computer and gave me his Sapphire HD 2600XT video card. He swears its 8X, yet Sapphire's website shows the specs on this card to be 4X/8X. I'm not sure I should install the video card for fear of burning out my mobo.

Thoughts?
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### #2 makai Posted 20 February 2009 - 04:19 PM

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LOL!

With all your AGP questions, I was wondering when you would get around to this one! I knew it was coming sooner or later!

Your motherboard supports 1.5v AGP 2.0. Therefore, this means that any video card you install must have the 1.5v slot. If you install a 4x/8x video card, and it has the 1.5v slot, then it means that it will accept the 1.5v your motherboard is putting out.

The voltage requirement of the video card is the important factor. According to this photo of the card, it does have a 1.5v slot, so it will handle the 1.5v from your motherboard.

Neither your motherboard or the vid card will fry... of course, I won't guarantee it! LOL! You just never know.

Read about things HERE... and if you get the warm fuzzies... go for it!
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### #3 Webslinger64 Posted 20 February 2009 - 04:46 PM

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Makai...I had a feeling you might answer this post. Your reply clarified a lot and the link you provided was excellent. I have one other question for you though. This illustration

shows video cards with a 3.3V slot, a 1.5V slot and one with a 3.3V and 1.5V slot. What about a video card that runs 0.8V? Is that slotted differently or is 0.8V compatible with either 1.5V or 3.3V, or both?

(Edit #2) Sheesh...ok, so are all video cards advertised as AGP 8X compatible with a 4X 1.5V AGP slot? For some reason, I'm under the impression that all AGP 8X video cards are 0.8V.

So as an example, the above pic is of an EVGA Nvidia 7800 GS, 256 MB, AGP 8x. Obviously, the card has a 1.5V slot, so it will fit in my AGP slot. So even though the card is advertised as "AGP 8X", as long as it has the 1.5V slot, it will work with my system right?

Edited by konakula29er, 20 February 2009 - 05:20 PM.

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### #4 makai Posted 20 February 2009 - 05:21 PM

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The "specification" for 8X cards is .8v. This means that all motherboards spec'd for 8X cards will have a AGP voltage of .8. However, the video card manufactures want to get the best bang for the buck, so they design the cards to be able to also run on 4x boards... thus modern AGP cards have the 1.5v slot so people with AGP 2.0 can also run that same 8x card.

Only two things to remember...

What is the motherboard AGP spec.
Does the video card have the required slot for the motherboard AGP spec.

By the way, they didn't add a slot for 8x cards... probably ran out of room... so, only the manufacture specs will tell you if its 8x or not.

Edited by makai, 20 February 2009 - 05:21 PM.

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