*ROM 7: Burnin' Rubber ROM 3
By default, just like on Amstrad CPC, if there are no peripherals issuing ROMDIS=HIGH, then BASIC (or more precisely: Physical ROM 1) is mapped to all logical ROM banks (in range of 00h..7Fh).
And on 6128+ only, physical ROM 3 is mapped to logical ROM 7. The ASIC is configured not to map it on 464+ and GX4000, even if a 6128+ cartridge is inserted.