CMOS: What It Is – howtosmash

CMOS: What it is?

Also known as CMOS, RTC (real-time clock), NVRAM (non-volatile RAM) or CMOS RAM. CMOS stands for complementary metal-oxide semiconductor. 


CMOS is an onboard, battery powered semiconductor chip to store information inside computers. If you look at the range to store, it stores from system time and date to system hardware settings. 


The most common CMOS coin cell battery (Panasonic CR 2023 3V) is the one used to power up the CMOS memory.

“Did you know that, CMOS is the short form
Complementary  Metal-Oxide Semiconductor

History of CMOS

The Motorola 146818 chip is the first RTC and CMOS RAM chip


Used in early IBM computers. This could store a maximum of 64 bytes of data. Because the system clock used 14 bytes, there are 50 bytes left to store system settings.


Today, most computers have moved their settings from CMOS and integrated into southbridge or super I / O chips.

How long this CMOS battery last?

The standard life time of a CMOS battery is about 10 years. But this depends on the usage and the environment of the computer.

Devices using CMOS?

Digital Logic circuit

SRAM (Static RAM)





How do we know if our CMOS battery is failing?

Failure of the CMOS battery means that our computer cannot keep the exact date and time.


When the CMOS battery fails, we see several indication messages,


CMOS Read Error

CMOS Checksum Error

CMOS Battery Failure


System Battery Voltage is Low

Reference : Google, Wikipedia

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