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I've heard the term "Tickless OS" thrown around.
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On a tick-less system, rather than waking up 100 times a second to see if anything is ready to process, the OS will look at when the next timer is due to expire and then sleep until that time.
The XNU kernel in Mac OS X 10.4 on, and the NT kernel in Windows 8 on, are also tickless. The Solaris 8 kernel introduced the cyclic subsystem which allows arbitrary resolution timers and tickless operation. FreeBSD 9 introduced a "dynamic tick mode" (aka tickless).
The FreeRTOS tickless idle mode stops the periodic tick interrupt during idle periods (periods when there are no application tasks that are able to execute), then makes a correcting adjustment to the RTOS tick count value when the tick interrupt is restarted.
To answer this - two cases are possible: idling CPU and non-idling CPU. If the CPU is idling, so no use of information are needed, and no updates, and therefore CPU will ignore updating it. This is called the tickless idling state. Was this worth your time? This helps us sort answers on the page. What is meant by kernel version?
A 'tick' in OS terms is an interval after which the OS will wake up to process any pending events.
So, if you have a 100Hz tick, then 100 times a second, the OS will wake up, check to see whether any timers have expired, execute their actions if there are, then go to sleep again. On a tick-less system, rather than waking up 100 times a second to see if anything is ready to process, the OS will look at when the next timer is due to expire and then sleep until that time.
Note that when the CPU is active, it's obviously not going to go into any kind of sleep mode, and the kernel will set up an interrupt for scheduling purposes. It's only tickless (as the comment points out) when there's nothing running on the CPU or (in very modern Linux kernels) when only one process is running.
Linux can run with or without ticks, with a compile-time switch. I don't know about any other systems.
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