what is a 100 nanosec unit -- my_getsystime()

[MARK CALLAGHAN]

I stumbled across this comment.
What is a 100 nanosec unit? Why was that used instead of nanosecs or microsecs?

/* get time since epoc in 100 nanosec units */
/* thus to get the current time we should use the system function
   with the highest possible resolution */
...
ulonglong my_getsystime()
{
...
}

-- 
Mark Callaghan
mdcallag@stripped