Gigabyte GA-586TX3 User Manual page 66

optional from chipset design. Video Shadow will increase the video
speed.
The default value is Enable.
Enabled Video shadow is enabled.
Disabled Video shadow is disabled.
C8000 - CFFFF Shadow / D0000 - DFFFF Shadow
These categories determine whether optional ROM will be copied to
RAM by 16 byte. The default value are Disabled.
Enabled Optional shadow is enabled.
Disabled Optional shadow is disabled.
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BIOS Configuration