Member Avatar for sathya691


Even after shutting down the system ,how the System manages
the CORRECT time.
How the clock "ticks" in the computer even there is no power supply.

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Short answer: a tiny, battery-backed real-time clock (RTC) on the motherboard keeps counting when the PC is powered off. pointed to that hardware piece — the notes below explain how it actually “ticks,” how the OS uses it, and what to do when time starts drifting.

The RTC is a small chip driven by a low-frequency crystal (commonly 32.768 kHz). That oscillator and a tiny amount of backup power let the chip count seconds continuously even with the main PSU unplugged. The same backup power also preserves a few firmware settings that the motherboard keeps in nonvolatile configuration storage (what people often call the CMOS settings). Battery life is limited (commonly several years), and a dead backup cell produces symptoms like wrong time at boot or lost BIOS settings.

At boot the operating system reads the RTC and sets the system clock. Once running the OS keeps time using the CPU/timer subsystem and corrects drift using time synchronization services (NTP or the Windows Time Service). If a computer is networked, periodic sync with public or local time servers will fix any RTC drift automatically; otherwise small inaccuracies accumulate over time.

Quick checks and fixes:

# Linux
timedatectl status
hwclock --show

# Windows (elevated CMD)
w32tm /query /status

If the clock resets after unplugging, check the backup cell voltage (around 3 V for common coin cells) and replace with the same type, powering down and unplugging first. On laptops the backup may be integrated or handled differently, so follow the service manual. After replacement, set the BIOS/UEFI time and let the OS resync. For more on RTC hardware and network time, see the Real-time clock overview and NTP documentation: Real-time clock (Wikipedia) and Network Time Protocol (NTP).

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Member Avatar for Rik_

There is a CR2032 battery on your motherboard that keeps the system clock active. It also keeps your bios active so it can store your pc's information.

Member Avatar for sathya691

Thanks for your valuable response

Member Avatar for Rik_

No problem. You can mark this thread solved unless you need anymore info. :)

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