Nonvolatile BIOS memory refers to a small memory on Laptop motherboards that is used to store BIOS settings. It's known as non-unstable memory or NVRAM as a result of, after the system loses energy, it does retain state by virtue of the CMOS battery. When the battery fails, BIOS settings are reset to their defaults. The battery will also be used to energy an actual time clock (RTC) and the RTC, NVRAM and battery could also be built-in into a single component. The name CMOS memory comes from the expertise used to make the memory, which is less complicated to say than NVRAM. The CMOS RAM and the true-time clock have been built-in as part of the southbridge chipset and so they is probably not standalone chips on fashionable motherboards. In flip, the southbridge has been integrated right into a single Platform Controller Hub. Alternatively BIOS settings may be stored in the computer's Tremendous I/O chip.
The chipset built-in NVRAM capability is often 256 bytes. For that reason, later BIOS implementations might use a small portion of BIOS flash ROM as NVRAM, to retailer BIOS setup and hardware configuration data. At this time's UEFI motherboards use NVRAM to retailer configuration data (NVRAM is a portion of the UEFI flash ROM), however by many OEMs' design, the UEFI settings are nonetheless misplaced if the CMOS battery fails. CR2032 lithium coin cell. This cell battery has an estimated life of three years when power provide unit (PSU) is unplugged or when the PSU power swap is turned off. This battery type, unlike the lithium-ion battery, is just not rechargeable and making an attempt to do so could end in an explosion. Motherboards have circuitry preventing batteries from being charged and discharged when a motherboard is powered on. Different widespread battery cell varieties can last significantly longer or shorter intervals, such because the smaller CR2016 which is able to typically last about 40% much less time than CR2032.
Increased temperatures and longer energy-off time will shorten battery cell life. When changing the battery cell, the system time and CMOS BIOS settings may revert to default values. Undesirable BIOS reset may be prevented by replacing the battery cell with the PSU power change turned on and plugged into an electric wall socket. On ATX motherboards, the PSU will supply 5V standby power to the motherboard to keep CMOS Memory Wave Protocol energized whereas the system is off. Some computer designs have used non-button cell batteries, such because the cylindrical "1/2 AA" used in the facility Mac G4 as well as some older IBM Computer compatibles, or a 3-cell nickel-cadmium (Ni-Cd) CMOS battery that appears like a "barrel" (widespread in Amiga and older IBM Pc compatibles), which serves the identical purpose. These motherboards often have a 4 pin straight header, with pin 2 missing, for connecting to an external 3.6v battery, such because the Tadiran TL-5242/W, when their soldered-on batteries run out. Ni-Cd batteries tend to leak devastatingly after a interval of disuse, damaging elements and traces on the circuit board near the battery. Mueller, Scott (2004). Upgrading and Repairing PCS. Fisher, Tim. "What is CMOS? (CMOS & CMOS Battery Definition)". Mueller, Scott (2003). Upgrading and Repairing PCS. Mueller, Scott (2004). Upgrading and Repairing PCS. Yao, Jiewen