Linux time keeping - Timer interrupt, jiffies, xtime

Under Linux system time is measured in "ticks" since the system was stated up. One tick represents 10 milliseconds, so the timer interrupt is triggered 100 times per second. The timer ticks are stored in the variable -

unsigned long volatile jiffies

jiffies
~~~~~~~

Every time a timer interrupt occurs, the value of the variable is
increamented. jiffies is initialised to 0 when the system boots, and
is thus the number of clock ticks since the computer was tured on.