X86 Power On Sequence The CPU gets its startup address from an external circuit. This is normally a hardwired circuit containing the address 'C000'. The "Reset" button causes the CPU to simply jump to the same address this external circuit supplies. This address may contain any X86 assembly program. Normally, it is mapped to a ROM circuit containing the system's BIOS. An embedded X86 system may place a different chip here, with a completely different program. Now-a-days, the BIOS is actually placed on a re-writable chip (EEPROM or the like) to allow upgrading it using software means only.