The first version released was AGP 1.0 with a speed of 1x, which offered the following specifications: 32-bit bus width, operating at 66 MHz, providing a maximum bandwidth of 266 MB/s, & utilizing.3V. So, it can be seen that right out of the gate, AGP offered double the bandwidth of PCI.
Each speed increase over 1x provided double the bandwidth as well as double the clock speed through the use of special signaling. So, AGP 2x offers a maximum bandwidth of 533 MB/s at a speed of 133 MHz, AGP 4x offers a maximum bandwidth of 1066 MB/s at a speed of 266 MHz, & AGP 8x offers.1 GB/s at a speed of 533 MHz.
Given the timeline of the evolution of these cards, AGP 8x cards dominate today's marketplace. Finding some cards that are backwards compatible is feasible, but the tricky part may be ensuring that the slot on the motherboard will accept them. Comparing the connector on this 128MB Apollo GeForce FX6600 GT card, to the connector on this 64MB Hercules 3D Prophet Ultra II card, & to the connector on this 256MB Chaintech GeForce FX5200 card shows that the first is obviously different than the second. The Apollo card is 8x only, the Hercules card is 4x/2x compatible, & the Chaintech card is 8x/4x, which ends up in different notches in the connector.
AGP 1.0 only features a.3V connection, the release of AGP 2.0 saw the availability of both a.3V &.5V connector, & AGP 2.0 makes use of the same.5V, but only requires 0.8V for signaling. In order to protect cards of different voltages/formats, special keyed connectors were designed so that only the correct card could be installed on any motherboard. A universal connector was finally released for AGP.0/2.0 which allowed cards of either voltage to be installed. For a schematic of the various connectors, visit this page. Although AGP.0 can share in the use of a universal connection, plenty of motherboards now only support 4x/8x cards based on the AGP.0 standard.
Another specification for AGP was released between 2.0 & 3.0, & was often called AGP Pro. AGP Pro was meant to be the new standard to meet the demands of high powered graphics workstations, but it never garnered widespread acceptance. Speeds of 1x, 2x, & 4x were supported with AGP Pro, & it utilized either a.3V, 5V, or a universal connector, similar to AGP 2.0. But, the AGP Pro connector was not the same size as the 'standard' AGP connector (see schematic at link above), meaning there were now more feasible connections to think about. An AGP Pro connection is longer than a standard AGP connection, & depending on the connector type, it could accept AGP 2.0 & 1.0 cards.
Modern motherboards supporting AGP will specify what type of card is compatible with the board, so the guess work is eliminated when trying to match with the other. For example, this Socket 754 Chaintech motherboard specifies that it is AGP 4x/8x slot & this Biostar LGA 775 motherboard specifies that it is 8x AGP slot.
Final Words
The AGP slot provided a much-needed boost to graphics cards as compared to the PCI slot, but game developers still managed to push the capabilities of this more powerful format to the edge. Something even faster was needed, & the next Tech Tip will take a glance at that something in "PCI Express." PCI Express is not only destined to be the successor to AGP 8x, but due to its flexibility, perhaps to PCI as well.
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