Why Your Computer Displays Correct Time Even When Turned On After Years

Wondered why your PC/laptop shows correct time even after being switched on after a year? Here is why!

Have you noticed a strange thing with your rarely used PC/laptop? If you have not used your PC/laptop a long period and you switch it on one day to find that it shows correct time? How can it do so without being connected to any electric outlet?

The reason for this is a timekeeper chip known as Real-time Clock or RTC. RTC is a semiconductor chip present on the motherboard which is assigned the job of keeping a note of the time when the computer disconnects from the power source. The Real-time Clock (RTC) or the CMOS ( Complementary Metal-oxide Semiconductor) chip by some manufacturers. In case it is a CMOS chip (known as CMOS RAM) it stores BIOS information of the computer in addition to the time. The RTC and CMOS have a very volatile memory and is powered by a CR2032 3V low voltage battery having a life of around ten years.

On desktop computers, the battery looks like a silver colored coin and is housed in the CPU itself or sometimes in the ATX tower.

Image result for cr2032Image result for computer with cr2032

The RTC chip is in compact form and irreplaceable, but you can replace the 2032 button cell if it gets exhausted.

Nowadays, the functions of 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. Single board computers like the Raspberry Pi or Android smartphones and iPhones don’t have RTC real-time clock chip. This is done to save the valuable space as well as sync time using Internet.

Older feature phones had the RTC powered by the mobile phone’s main battery. That’s the reason that every time you switched on or removed battery from your Nokia 1100, you had to set up the time and date.

How does Apple’s Mac keep time?

Apple’s Macs have their own distinct architecture to support the time function. In older Macs, the time is managed by a chip called PRAM or Parameter RAM. Similar to Windows run PCs, the PRAM chip on Macs is powered by a battery and keeps date and time information on the Macintosh machines. On newer Macs, the place of PRAM is taken by NVRAM (Non-Volatile RAM) which doesn’t require any battery to keep the data alive. The NVRAM can also store information, quickly like the screen resolution, speaker volume, startup disk selection, etc.

With Internet becoming a cornerstone of technology, the older RTC chips have given way to NTP Internet time.  Network Time Protocol (NTP) is a networking protocol for clock synchronization between computer systems over Internet. It has been in operation since 1985 and was designed by David L. Mills of the University of Delaware. NTP is so powerful that it synchronizes all connected computers to within a few milliseconds of Coordinated Universal Time (UTC). It uses a modified version of Marzullo’s algorithm to select accurate time servers and is designed to mitigate network latency. NTP can usually maintain time to within tens of milliseconds over the public Internet, and can achieve better than one millisecond accuracy in local area networks under ideal conditions.

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