    Basically the first jap ps2 had a single bios and the dvd player etc were installed on the memcard.
    The Ps2's after that first model had the Dvd Player software installed in a separate ROM (EROM) which is encrypted.
    The ROM1 is an additional part of the BIOS that contains some extra stuff like ID's for DVD Player version etc.
    ROM2 is the same really but I think only available in Chinese PS2's.
    Hope this helps.

A new Bios dumper is already available that can dump your PS2 Bios,ROM1,ROM2,EROM and NVM. Get it HERE

Note: For maximum compatibility it is recommended that you use a BIOS image different than SCPH10000.BIN which is the
 oldest one. That's because with this BIOS there are problems in memory card emulation and in other sections.

BIN EROM ROM1 ROM2 NVM

DIFF.bin EROM.bin ROM0.bin ROM1.bin ROM2.bin  NVM.bin

On newer consoles "EROM" & "ROM2" are missing since they are unused,
 and "ROM1" is only required for using the PS2's LD-player,
 which is something PCSX2 can point out with a message.

only need ROM0 ROM1 NVM

