If you ignore the legal advice and search for a direct download, be extremely careful. The ROM/BIOS download scene is riddled with malware. Avoid:

Legitimate scene releases are usually archived in .zip or .7z files containing only .bin and .nvm files.

Unlike modern PC games, the PlayStation 2 did not contain all its operating system on the game disc. Instead, core functions—like memory card management, DVD playback, and boot sequence—are stored on a ROM chip inside the console. Emulators like PCSX2 cannot legally or functionally run without a BIOS image.

The SCPH-70004 BIOS is popular for several reasons:

Once you have obtained the file (whether legally or otherwise), using it in the PCSX2 emulator is straightforward:

If you're having trouble finding or downloading the specific BIOS file you need, consider:

There are several reasons why someone might want to download a BIOS file like scph-70004-bios-v12-eur-200.bin: