As the battery aged, the electrical charge that maintained the CMOS settings diminished.The BIOS and RTC would then revert to its default settings, resulting in, "Press F1 to enter the CMOS setup." Note: The terms CMOS setup and BIOS setup were frequently used interchangeably in the 1990s and far into the 2000s. UEFI is an acronym for Unified Extensible Firmware Interface.The CMOS and Real-Time Clock (RTC) required an electric charge to maintain their settings.
This would imply that a BIOS would work across main boards that use the same processor and chipset.However, slight design differences from one main board to another make this not true.Note: The main board is commonly referred to as a motherboard in the PC industry.In Apple® computers, it is referred to as the logic board.
Note: Boot speed, boot efficiency and size in Bytes are also taken into consideration when a BIOS is ported.
Historically, the BIOS and its settings were stored into CMOS (complementary metal-oxide semiconductor) and was commonly referred to as the CMOS Setup.