x86 BIOS chip reading?

After doing some research, I've found out that the BIOS chip is loaded at FFFF:FFF0 minus the BIOS ROM size (so F000:0000 with 64K, E000:0000 with 128K ROMS). How does this work with 128KB+ ROMS?
I assume they're either mapped with banks or reading them using some port I/O. Anyone knows how this is done?
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