My phone was switched off since the past hour and I switched it on right now and I realised how normal it was for It to show me the exact present time and date and I wonder how.
In: Technology
It has a battery-backed clock on the inside. You don’t *have* to sync your time with the internet, and you don’t always have an internet connection. If you don’t, the phone still keeps relatively decent time while it’s on. How?
There’s a circuit somewhere in the phone that serves as a clock. It might even be part of the CPU. One neat thing we figured out a long time ago is certain crystals vibrate at predictable frequencies when you run electricity through them. That’s why you see a lot of watches say they have a “quartz movement”. Both watches and computers take advantage of this.
So basically a tiny quartz crystal gets installed in a thing that can count how many times it vibrates. Then some electricity is applied. The person who designed the circuit set it up so once the right number of vibrations happens, a “tick” happens. That “tick” might be once per second, but usually it’s much faster so smaller amounts of time can be measured. The smallest amount of time that can be measured is whatever one vibration of that crystal takes.
So even when your phone is “off”, it’s probably still running a tiny circuit that updates the clock. This only takes a teeny tiny amount of electricity. Many simple watches can go 3+ years on one battery charge. So your phone can stay off for a long time before that clock circuit drains the battery.
PCs have this too. If you open most cases, you’ll find a small watch battery attached to he motherboard. This is used to keep the clock running even when there is no power. There’s also a battery inside some early Game Boy games like Pokemon Crystal that had a clock. By now many of the batteries have run out and those clock-based features don’t work anymore if you turn off the game! Pretty much anything that has an “off” state and keeps the time is likely using a small battery-backed quartz clock to do so.
These clocks aren’t always the most accurate, though. Very accurate ones are more expensive. That’s why computers tend to sync with an internet time source. My last PC could be as much as 5 minutes wrong if it went a day without internet connectivity.
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