The Advanced Graphics Riser is a variation of the
Accelerated Graphics Port (AGP) used in some
PCIe motherboards made by
MSI to offer a limited backwards compatibility with AGP. It is, effectively, a modified PCIe slot allowing for performance comparable to an AGP 4x/8x slot,
but with limited support of AGP cards. The manufacturer has published a non-exhaustive compatibility list of cards and chipsets that work with the modified slot.
References
Motherboard expansion slot
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