10.6. The Software Clock (Jiffies)

The accuracy of various time-related system calls described in this book is limited to the resolution of the system software clock, which measures time in units called jiffies. The size of a jiffy is defined by the constant HZ within the kernel source code. This is the unit in which the kernel allocates the CPU to processes under the round-robin time-sharing scheduling algorithm (Section 35.1).

On Linux/x86-32 in kernel versions up to and including 2.4, the rate of the software clock was 100 hertz; that is, a jiffy is 10 milliseconds.