Intel SG-81 - Manual (Page 19)

Hardware Setup 2-9
2.3.7. Accelerated Graphics Port Slot (AGP1)
This slot supports an optional AGP graphics card up to AGP 8X/4X mode.
ATTENTION: This motherboard does not support 3.3V AGP cards. Use only 1.5V
or 0.8V AGP cards.
User’s Manual