please Explain AGP voltages

**uncleel** · January 5th, 2003, 01:16 PM

I'm confused about AGP voltages
I'd like to put a GeForce4 MX (budget minded)
on an ECS K7SEM, (4X agp) but the documentation is so sparse.

I understand if you have an older AGP 2X or 1X system
a 4X -or-8X card may not work, because of varying voltages.
While a 2X-4X mobo (ie: Abit KT7) should be ok

Is the AGP voltage a Bios enabled thing, -or- are the cards themselves limited?

Can someway explain in simple terms.

**Kruzin** · January 5th, 2003, 02:52 PM

Some motherboards do 3.3v AGP (older 1x/2x)
Others do 1.5v AGP (newer 4x/8x)
Some video cards only do 3.3v, some only do 1.5v, some will do either.
Among those that will do either voltage, some are automatically switching, some require a jumper on the card to be changed.
The AGP slot/edge connector is keyed so that only the proper card will fit in the proper slot (with the cards that will run either voltage keyed to fit in either type slot).

**Peter M** · January 5th, 2003, 03:01 PM

Unmix the issue, and all will become clear.

The SUPPLY voltage to AGP cards is and has always been 3.3V.

The SIGNALLING voltage used to be 3.3V in 1x/2x, is 1.5V in 4x, and 0.8V in 8x mode.

To prevent people from plugging incompatible stuff together, the slots and cards are keyed. See the below ATi link for nice illustrations ... and note that plenty Intel 845 series boards screw up on this, having a "universal" slot although the chipset is 4x-only. Toast time ...

http://mirror.ati.com/support/faq/agpchart.html