8x AGP graphics cards not backwards compatible?

[Damrod]

I wondered... all the new cards from ATI state as requirement "Power Mac G5" (the X800 for exmple), but I wondered why? Isn't AGP basically backwards compatible so that an AGP 8x card can work in an AGP 4x slot?

 

[nixgeek]

Most AGP 8x cards will work down to 4x, but they run at a voltage of 1.5. If the previous systems used AGP cards at a voltage of 3v, they won't work. You can actually do damage to the card and/or motherboard if you do this. I mistakenly installed an older AGP card to a PC motherboard that supported AGP 8x. Thankfully nothiing bad happened. The motherboard suported the 1.5v AGP and the card was a 3v AGP card.

 

[Damrod]

Ah, so if I get this right:

For example the ATI Radeon X850 is labeled G5 only, as my mainboard in the G4 MDD is not cabable of delivering the right voltage to the card?

 

[ElDiabloConCaca]

Correct.

 

[Damrod]

Ah, ok. Thanks for clearing that up