Have you noticed something strange happening on your rarely used PC/laptop?
If you haven't used your PC/laptop for a long time and you turn it on one day, you will find that it shows the correct time. How is this done without being connected to any electrical outlet?
The reason for this is a timing chip known as a real-time clock, or RTC. The RTC is a semiconductor chip located on the motherboard that is responsible for noting the moment the PC is disconnected from the power source.
The clock (RTC) or CMOS chip by some manufacturers. In the case of a CMOS chip (known as CMOS RAM) it stores the computer's BIOS information in addition to the time. The RTC and CMOS have a highly volatile memory and are powered by a CR2032 3V low-voltage battery that has a lifespan of around ten years.
In desktop PCs, the battery looks like a silver coin and is housed in the CPU itself or sometimes in the ATX tower.
The RTC chip is in a compact form factor and non-replaceable, but you can replace the 2032 if it runs out.
Nowadays, the functions of the RTC have been taken over by NTP time servers. If you have set your time settings to automatic, the computer will connect to the NTS time servers and display the exact time. Computers like Raspberry Pi or Android smartphones and iPhones do not have an RTC chip. This is done to save valuable space, as well as synchronization time using the Internet.
Older phones had RTCs that were powered by the main battery of the mobile phone. This is why every time you turned off or removed the battery from your Nokia 1100, you would have to reset the time and date.
Apple Macs have their own unique architecture for supporting the time function. In older Macs, the time is managed by a chip called PRAM, or Parameter RAM. Similar to Windows-based computers, the PRAM chip for Macs is powered by a battery and maintains date and time information on Macintosh machines. In newer Macs, the PRAM space is taken up by NVRAM (non-volatile RAM), which does not require a battery to hold data.
