TapAGP muddle

This discussion is about ordinary AGP graphics cards, it does not consider the latest, most powerful gaming cards available; these often have extra special requirements and connectors. I am also not considering PCI Express (PCIe) cards. Motherboards either accept AGP or PCIe, but rarely both.

Disregarding the “pro” types, there are three main types of AGP graphics standard: AGP 1.0 operating at 3.3v and supporting 1x and 2x speed; AGP 2.0 operating at 1.5v and supporting 1x, 2x and 4x speed; and AGP 3.0 operating at 0.8v and supporting 4x and 8x speed. Individual cards and motherboards can, however, support more than one standard.

Will it fit?

That depends on the slots in the card and keys in the socket on the motherboard. These are there for safety. In general, if a card fits then it will not damage either the graphics card or the motherboard. However I give no guarantees here, some cards and boards do not obey the rules, beware of no-name budget models. There are two slots and corresponding keys. The 3.3v slot is about a third of the way along from the back end of the connector, and the 1.5v slot is about 2/3 of the way along. There is no 0.8v slot, this is worked out automatically. If a socket has no keys (called “Universal”) then it should safely accept either. In the same way that if a card has both slots (also called “Universal”) then it should be safe in any socket.

Another practical consideration is the thickness of the card and its components. Some are so fat that they occupy all or part of the space that should be available for the adjacent PCI slot.

Will it work?

The fact that a card may fit and not damage either itself or the host does not mean that it will function. There are terms that are defined by the standards to describe them, but are often misused or ignored by the manufacturers.

Here is a simple table to try and determine if it will work. The first column shows the terms that should be used to describe the interface. The second column shows what the connector should look like so compare it with the actual devices (or pictures), The last column shows the available accelerator speeds. Manufacturers are better at giving these figures than any others. So long as it fits and there is overlap in both the operating voltage and the available speeds then the card should work in the slot.

Motherboard/Card Connector Available speeds
AGP 3.3V 3.3V key/slot 1x, 2x at 3.3V only
AGP 1.5V 1.5V key/slot 1x, 2x, 4x and 1.5V only
Universal AGP Universal 1x, 2x at 3.3V and 1x, 2x, 4x at 1.5V
AGP 3.0 1.5V key/slot 4x, 8x at 0.8V only (electronic detection to prevent 1.5V operation)
Universal 1.5V AGP 3.0 1.5V key/slot 1x, 2x, 4x at 1.5V and 4x, 8x at 0.8V
Universal AGP 3.0 Universal 1x, 2x at 3.3V, 1x, 2x, 4x at 1.5V and 4x, 8x at 0.8V

For example – I am trying to fit a Matrox P650 card to my machine which has a Gigabyte K7 Triton GA-7VKMP motherboard. The motherboard manual says that it has a AGP 4x slot. Looking at it, it has no keys in the socket so I am inclined to think it is “Universal AGP”. The graphics card is described as AGP 3.0 supporting 8x, 4x, 2x and 1x* operation. The picture of the card has a 1.5v slot. This doesn’t fit the specification for “AGP 3.0” as it supports 2x operation, it has only the one slot so it is not “Universal AGP 3.0” so it looks like it is actually “Universal 1.5v AGP 3.0”. The conclusion is that I expect it to work; at 1.5v 4x speed. There is footnote * by 1x in the Matrox specification but I can’t find the footnote.

Playtool have some good charts and a lot of detailed notes to fully explain the position and this quote resolved the bulk of questions immediately “nobody makes AGP 3.0 cards, and nobody makes AGP 3.0 motherboards …Every single video card I could find which claimed to be an AGP 3.0 card was actually a universal 1.5V AGP 3.0 card. And every motherboard which claimed to be an AGP 3.0 motherboard turned out to be a universal 1.5V AGP 3.0 motherboard.” Which simplifies the situation no end because it becomes true that “If an AGP card fits in an AGP slot then they are compatible”—a great reassurance. This link also conveniently lists most AGP cards and their true type.

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