epsxe000.mcr acts as a virtual EEPROM. When ePSXe launches a game (e.g., Final Fantasy VII , Metal Gear Solid ), the emulator intercepts BIOS calls to the memory card port and redirects read/write operations to this file. This allows:

By default, epsxe000.mcr is assigned to Memory Card Slot 1, while epsxe001.mcr typically occupies Slot 2.