A Practical Perspective
Let's look into the practical perspective of clocks and time in distributed systems.
The clocks used in real systems are what we usually call physical clocks.
Physical clock
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Most physical clocks are based on cyclic processes. Below are some examples of such devices:
Sundial
A sundial is one of the most basic and easy-to-understand devices. It tells the time of the day by using a gnomon and tracking the shadow created by the sun.
Hourglass
An hourglass is also a basic and easy-to-understand device. It measures time by the regulated flow of sand through a bulb.
Pendulum clock
A pendulum clock is a common clock device that uses an oscillating weight as its timekeeping element.
Quartz clock
A quartz clock is an electronic version of the pendulum clock and is used in software systems. This device makes use of a crystal, called quartz ...