realtime clock (RTC)
Precise real-time clocks(RTC) are used in a wide variety of systems and devices in communications technology. For example, in servers, communication networks, measuring devices and backup systems.
Most real-time clocks have as their time standard a clock signal of 32.768 kHz, which is generated by a quartz crystal and from which the time reference and the date are derived. Since crystals with such low frequencies are dependent on temperature variations, the crystal circuits must be temperature compensated. Personalcomputers have by default a real-time clock on the motherboard via which the date and the current time are displayed in hours, minutes and seconds. The date and time are set in the BIOS and can be displayed and set via the system functions date and time.
The real-time clock can be obtained from a clock generator and is buffered by a battery so that it continues to run even when the computer is switched off or disconnected from the supply voltage. In networks, it can also be synchronized to the server 's real-time clock.
The real-time clock can be configured by software and takes into account the changeover from winter to summer time.