P ROM
16bit ROM(s) containing byteswapped 68k binaries in cartridges.
Sometimes, two 8 bit ROMs are used as a second P ROM (called "SP1/2" or "EP1/2").
When unbanked, the maximum size is 1MiB. Some games use bankswitching to use 2MiB or bigger P ROMs.
Some cartridges use an NGPC flash board soldered in place of the mask ROMs.