P ROM
16bit ROM(s) containing the byteswapped 68k program in cartridges.
Sometimes, two 8 bit ROMs are used as a second P ROM (called "SP1/2" or "EP1/2").
When not banked, the maximum size is 1MiB. Some games use bankswitching for 2MiB or larger P ROMs.
Some cartridges use an NGPC flash board soldered in place of the mask ROMs.
Speed
Minimum speed: 150ns. Can use slower ROMs by using the cartridge's wait cycle configuration.