On the motherboard, as shown below
Extending knowledge about CMOS lithium batteries
In computing, CMOS often refers to storage Basic computer startup information (such as date, time, startup settings, etc.). Sometimes people confuse CMOS and BIOS. In fact, CMOS is a readable and writable RAM chip on the motherboard, which is used to save the BIOS hardware configuration and user settings for certain settings. The CMOS can be powered by the motherboard battery, so even if the system loses power, the information will not be lost. CMOS RAM itself is just a piece of memory and only has the function of saving data. Adjusting various settings in BIOS requires special procedures. The BIOS setup program is usually built into the chip by the manufacturer. You canz Access the BIOS setup program by pressing specific buttons when turning on the computer, making system setup easier. This is why BIOS settings are sometimes called CMOS settings.