Function:

RDTSC reads a Pentium internal 64 bit register which is being incremented
from 0000 0000 0000 0000 at every CPU internal clockcycle. Note that this
gives a clockcycle-accurate timer with a range of more than 8800 years at
66 Mhz...

The instruction places the counter in the EDX:EAX register pair.




REPNC / REPC  Repeat next string operation while (No) Carry
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