Nonvolatile BIOS memory

The term CMOS RAM, CMOS static RAM actually (English ) refers, in computer engineering or computer industry has a battery-backed SRAM CMOS technology, in which the BIOS parameters are stored. The battery backup is necessary because otherwise the settings / information would be lost or reset to the default settings.

The abbreviation comes from the fact that CMOS SRAM usually with a complementary metal oxide semiconductor (English, CMOS) static random-access memory (English, SRAM) has been implemented. The shortened term " CMOS RAM " or even " CMOS" are due mainly to inaccuracies in the handling of the terms.

Power supply

The CMOS RAM and the PC clock (called regarding the function and CMOS battery) usually powered by a CR2032 lithium battery. These batteries should last, depending on the motherboard, the ambient temperature and the disconnection of the PC usually between two and ten years. Higher temperatures and longer times at which the PC is turned off, to shorten the battery life.

If the battery for the CMOS RAM is changed, the system time and CMOS RAM can be reset. That is why it is generally recommended to change the battery when the AC adapter but the computer is off. For motherboards in ATX format so that a supply voltage of 3 V is supplied, making the CMOS RAM is supplied without battery.

Not always is a coin cell CMOS battery used - so there is for example, computers with cylindrical 1/2-AA-Batterien ( for example, in the Power Mac G4 Cube ) or 3 -cell NiCd batteries in the form of small metric tons (eg, in Amigas ).