I/O processor - MIPS R3000A (PS1 main processor) used in all console models since SCPH-700XX.
PowerPC 405 chip that replaced IOP. Chip include 4MB SDRAM. In IOP emulator mode 2MB are used as a IOP memory. In PS2 used since SCPH-750XX model. New chip require some compatibility tweaks that are done per title by xparam file found in PS2 ROM.