Users can configure ticks per second for real-time clocks. The define TICKSPERSEC in the /usr/include/conf.h file defaults to 100 ticks per second (which leads to 10ms between ticks).
Recommended minimum and maximum ticks per second are 20 (50 ms between ticks) and 500 (2ms between ticks).These numbers can vary depending on a systems hardware limitations.
It is possible to add hardware timers, they are handled by specific drivers interfaced with the POSIX timer.