Invoking Cunningham's, I'd guess it's memory mapped I/O occupying 0xE0000000 - 0xFFFFFFFF. That's the top ⅛ of the address space, which is every binary address

Invoking Cunningham's, I'd guess it's memory mapped I/O occupying 0xE0000000 - 0xFFFFFFFF. That's the top ⅛ of the address space, which is every binary address starting with 111. In researching this I learned that some 32bit hardware could utilize 128GB of ram using Physical Address Extensions. Each process is still limited to 4GB though.