Why computer didn't use cesium atom to define 1 second?

Question

As far I know computer using crystal oscilator to define 1 second and it's not real 1 second, i mean it's not stable.

While real clock using cesium and we know cesium is stable, why doesn't computer contain cesium in its component to define 1 second.

So thats mean 1 second in clock atom and 1 second in computer are not syncreon, even 1 second at between two computers are not syncreon each other.

What I mean with computer is not only advanced computer device like personal computer, this applied to microcontroller.

Instead of using atom cesium, they are using Internet Protocol especially Network Time Protocol (NTP)

I'm wonder is there fatal effect from asyncreon of computer time like maybe airport schedule or what if they didn't use NTP.

Answer 1

First of all, the reason personal computers dont't use atomic clocks based on caesium is price. One CSAC (chip scale atomic clock) costs 5000 USD nowadays. The added precision is not worth the price for the normal consumer. However there are cases where the time synchronization via NTP combined with a crystal oscillator are not precise enough. For example missiles that rely on GPS to determine their location / find their target use CSACs to get much higher GPS precision.
Other applications are for example radar, or scientific measurements.