Most modern computers have atleast 3 to 4 clocks in their motherboards to do different kind of operations.
For example in my HP motherboard I got 4 clocks.
First One 14.31818Mhz used for CPU and other operations in motherboard, second is 25.000Mhz for HDD and DVD ROM, Third is also 25.000Mhz for Ethernet and the Fourth is 32.768Khz used as a realtime clock.
The attacker can measure the target’s clock skew by obtaining timestamps from the target’s clock and comparing these timestamps against the local clock.
So my question is which clock in our PC sends the timestamps?