This week TechARP discusses the ISA Enable Bit BIOS feature, a setting you may find on older motherboards.
You can read about it over here.
This BIOS feature allows you to determine if the system controller will perform ISA aliasing to prevent conflicts between ISA devices.
The default setting of Enabled forces the system controller to alias ISA addresses using address bits [15:10]. This restricts all 16-bit addressing devices to a maximum contiguous I/O space of 256 bytes.
When disabled, the system controller will not perform any ISA aliasing and all 16 address lines can be used for I/O address space decoding. This gives 16-bit addressing devices access to the full 64KB I/O space.
It is recommended that you disable ISA Enable Bit for optimal AGP (and PCI) performance. It will also prevent your AGP or PCI cards from conflicting with your ISA cards. Enable it only if you have ISA devices that are conflicting with each other.