How do the clock function works in operating systems?

Question

I don't understand how clock function works within an operating system.

First the documentation for clock function in www.cplusplus.com is:

Returns the processor time consumed by the program.

The value returned is expressed in clock ticks[...] 

As far as I understand, the clock function must access directly some register within the CPU that is a counter for CPU cycles. How is this possible? I mean, any register of 32 bits would overflow very soon if it is being incremented one unit at the CPU frecuency. Is the OS handling this overflow in some way?

Answer 1

"Clock ticks" are implementation-defined, not in units of the cpu clock. Historically they were fixed-length, coarse-grained scheduling timeslices. There is no need for any special hardware TSC to implement clock . It suffices to simply count up the timeslices the process is scheduled for (which are ultimately enforced by a timer interrupt or similar).