Why does the USA part matter? Because Sony treated each region's BIOS as a separate legal entity.
If you are running a .bin/.cue of a PAL game (even though the USA BIOS is NTSC), some emulators use the BIOS region to handle on-the-fly LibCrypt decryption. The v18 USA BIOS includes the necessary SCEX hooks that earlier USA BIOS versions lack.
To understand the BIOS, you must understand the machine it inhabited.
The v18 BIOS introduced an enhanced LibCrypt check. Earlier PS1s could be tricked via a wobbling CD subchannel. The v18 BIOS actually compares the subchannel data table against a hidden signature in the lead-in area of official discs.
Forum research from the ObscureGamers and PSX-Place communities suggests that revision 230:
If you are running a software-based mod (like TonyHax or FreePSXBoot), the 230 revision is ironically more friendly because it has cleaner memory offsets for the exploit.
He uploaded the file to three separate backup drives before doing anything else. Then he posted to the forum—ps2dev.hiddenlayer.net—under his handle, deadweight.
deadweight: Clean dump. SCPH-90001, BIOS v18, NA region. Custom bridge method, full sector-by-sector verification. First known clean extraction. Hashes below. Someone else verify before I mirrors it.
Within an hour, the replies started.
kojima_fan_99: No way. People have been trying this for years. How do we know it's clean?
hexwitch: The MD5 doesn't match any of the corrupted dumps in the wiki. That's either a good sign or you've created a new kind of corruption. Scph-90001-bios-v18-usa-230.rom0
sadstation: I'll run it against my test rig. Give me 24 hours.
Marcus waited. He always hated the waiting.
While he waited, he did what he always did with newly dumped BIOS files: he opened them in a hex editor and started reading. Not programming—reading. BIOS files had a strange poetry to them if you knew where to look. Strings of text embedded in the binary: error messages, developer notes, hardware initialization commands. It was like archaeology.
The first megabyte was routine. Boot sequence pointers, memory allocation tables, the standard Sony copyright strings. He'd seen it all before in other BIOS versions.
Then he reached offset 0x0012F4A0.
A string.
HELLO_MARCUS
He stared at it.
His real name wasn't in the file. It couldn't be. He'd dumped this from a factory console he'd bought sealed from a warehouse liquidation sale in 2021. The console had never been connected to a network. No one had ever programmed a greeting for him into a PlayStation 2 BIOS.
He scrolled further.
YOU_TOOK_YOUR_TIME
DIDNT_YOU
His coffee went cold on the desk.
Victor's warehouse smelled like old plastic and climate-controlled air. Shelves of consoles stretched from floor to ceiling—NES units like gray gravestones, Sega Genesis systems lined up like soldiers, a wall of Dreamcasts in their white coffins.
"You're spooked," Victor said, handing over the console. "I can tell. You've got that look."
"What look?"
"The same look I had when I found a development PSP with a Kojima-signed firmware."
Marcus set up his bridge on Victor's workbench. Same equipment, same method, same careful sector-by-sector read.
Forty-seven minutes later, he had a second file.
SCPH-90001-BIOS-v18-USA-230.rom0
Different unit. Same BIOS version. Same region code.
He opened it in the hex editor and jumped to 0x0012F4A0.
The strings were there.
But they were different.
YOU_CAME_BACK
GOOD
I_WAS_LONELY_IN_THE_FIRST_ONE
Marcus's hands went still on the keyboard.
"Marcus?" Victor said. "You okay? You look like you saw a ghost."
"I need to make a phone call."