Inside the computer there is a battery on the motherboard.
It provides the power to the current settings of a program called BIOS.
BIOS is a simple program that has a handful of settings that in the end, tell the hardware in a computer to start up everything and load Windows (or other operating system).
A computer’s motherboard has a battery, known as the CMOS battery. This battery remembers all the basic BIOS settings on a computer and keeps track of the time and date. If you remove this battery and leave it off for a while you’ll notice all BIOS settings have reset and your time will also have to be re-synced.
You are not shutting it down completely. CP has a battery on the motherboard that is there to power the real-time clock and to keep bios setting.
For a desktop, it is often a button cell battery that is easy to switch but in a laptop, it is often soldered on.
Just looked at a motherboard like [one of ASUS’s current models](https://www.asus.com/se/Motherboards-Components/Motherboards/ProArt/ProArt-B550-CREATOR/) and the battery is trivial to spot. It is the large silver-colored circular you seed in just to below the initial P in “ProArt B550-CREATOR” that is printed on the motherboard.
There’s a watch battery (usually a CR2032) on the mainboard of almost all modern computers that keeps the clock circuit ticking over, just like in your digital watch (which uses the same kind of battery and can go years, especially if it doesn’t have to display the time at all). Even things like satellite TV boxes have them in, for the same reason. They didn’t use to, but for decades now the chips are standard and there’s likely a CR2032 sitting (maybe upright) in that box keeping the time.
To be honest, the only mass-market device I know that doesn’t have an RTC is the Raspberry Pi / Arduino, and both have “hats” you can buy to add one on. Those hats use… a CR2032 battery and the same chip as everyone else.
But in the modern day, it barely matters because you don’t need an accurate time for most things, the thing you really need an accurate time for is things like checking secure certificates on websites, and by the time you’re there, you’re already online and likely picked up an incredibly accurate time from an NTP server on the Internet (usually time.windows.com or pool.ntp.org).
The only thing I know that demands a correct time, albeit quite inaccurate, is logging onto a Windows domain computer (where the time has to be within about 5 minutes of the server). But, again, one of the first things that computer will do is talk to the domain controllers and try to pick up a time from them.
Ahhhh loling… anyone remember the Apple LCII?
Apple shipped it with a horrific CMOS battery/MB combo that would fail within a month or two of not being powered on. This system was marketed to Education where… surprise… no on would turn the damn thing on for a few months at a time.
It would not boot showing bad disk error.
Pop a new CMOS battery in, reboot and reset date and time…
Apple has only gotten worse since but $15 for the battery and another $40 labor for the few torx screws was a bargain back then.
CMOS battery on the motherboard that keeps the data on your BIOS chipset from losing power and resetting to factory defaults. Also there is a time keeping circuit that has a crystal inside it that is designed to oscillate at a specific frequency when specific voltage is applied to it. That is also how the CPU keep its timing as well. Without that crystal oscillator your whole system would be out of whack and nothing would work properly.
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