This is the bast site that explains it:

AGP compatibility for sticklers

I was reading some specifications on the G450 AGP and Parhelia 128MB AGP official legacy site and maybe I think I understood it right. Both cards has the usual opened 2x/4x socket,

BUT the G450 has specified this: AGP 4x, compatible with all AGP slots (0.8, 1.5, or 3.3 V)

the Parhelia 128MB has specified this: AGP 8x, compatible with all compliant AGP 4x and 8x systems (1.5 or 0.8 V)

So could the second card be damaged on an older AGP 3,3v only mainboard, while the first will not in any mainboards?

> So returning to the words written on my mainboard "3,3v AGP card will cause permanent damages", why this would happen if the 3.3v cards had the closed connector?

Maybe if somebody was trying to force the card into the slot? (And yes, such elephants do exist)

h-a-l-9000 wrote:

> So returning to the words written on my mainboard "3,3v AGP card will cause permanent damages", why this would happen if the 3.3v cards had the closed connector?

Maybe if somebody was trying to force the card into the slot? (And yes, such elephants do exist)

I think more the case where some manufacturer could use the AGP2.0 opened socket on a 3,3v only design. In that link they seems to think the idea of "any cards that fit should be ok" is not true.
The only way to know should be measuring the voltage the socket is actually giving to the cards but also we would not know if that voltage is regulated after or not. By the way I am trying a G450 AGP on the KT600 AGP8x board and it's running ok until now.

As it says, some manufacturers did violate the keying specifications, most likely a 1.5V only motherboard being keyed as "universal".
Also, some chipset / card combinations can be tricky, failed to work with a savage 2000 card in an AMD750 chipset motherboard, but then the AMD750 is not the greatest AGP chipset!!!!

Well, i found a quite strange motherboard, an Abit SG-72 which is based on the SiS 661FX chipset, but aparently it has an universal AGP port (SiS 661FX motherboards usually have 1.5/0.8 keyed slots). I just decided to pop some 3.3 v cards on that motherboard and none of them didn't work, one did actually made the system POST, but it was only a mess of random characters

The Abit SG-72 supports FSB 800 Northwood and Prescott P4s with HT, AGP 8x, DDR400, but is still quite strange an universal slot on that kind of motherboard. I haven't tried other cards nor universal/1.5/0.8 v only cards yet

I have some P4 boards with universal AGP too. Some work fine, they are compatible, the other ones won't post. One even has a warning LED if you put in the wrong card.

The documentation usually tells you if it's compatible or not.

PhilsComputerLab wrote:

I have some P4 boards with universal AGP too. Some work fine, they are compatible, the other ones won't post. One even has a warning LED if you put in the wrong card.

The documentation usually tells you if it's compatible or not.

There was nothing about 3.3 volt cards on my Abit SG-72 manual afaik. I know most older P4 also featured universal AGP slots (mainly SiS and VIA chipsets), but mainly, they only usually support AGP 4x, DDR up to 266 or 333 and only 400/533 FSB CPUs without HT (a few of them suspported the 3.06 Ghz HT model though), but my Abit is quite different... DDR 400, AGP 8x, FSB 800 Northwood and Prescott support.

I still need to do futher tests on that Abit

Yea in the manual or in the specifications. If it doesn't mention anything about 3.3V than likely it doesn't support it. Though I found many boards with that clearly being mentioned. Mostly AOpen boards though. I don't have anything from ABit with SIS chipset...